Chapter 4C. Traffic Control Signal Needs Studies
Section 4C.01 Studies and Factors for Justifying Traffic Control Signals
Standard:
An engineering study of traffic conditions, pedestrian characteristics,
and physical characteristics of the location shall be performed
to determine whether installation of a traffic control signal is
justified at a particular location.
The investigation of the need for a traffic control signal shall include an analysis of the applicable factors contained in the following traffic signal warrants and other factors related to existing operation and safety at the study location:
Warrant 1, Eight-Hour Vehicular Volume.
Warrant 2, Four-Hour Vehicular Volume.
Warrant 3, Peak Hour.
Warrant 4, Pedestrian Volume.
Warrant 5, School Crossing.
Warrant 6, Coordinated Signal System.
Warrant 7, Crash Experience.
Warrant 8, Roadway Network.
The satisfaction of a traffic signal warrant or warrants shall not in itself require the installation of a traffic control signal.
Support:
Sections 8D.07
and 10D.05
contain information regarding the use of traffic control signals
instead of gates and/or flashing light signals at highway-railroad
grade crossings and highway-light rail transit grade crossings,
respectively.
Guidance:
A traffic control signal should not be installed unless one or more
of the factors described in this Chapter are met.
A traffic control signal should not be installed unless an engineering study indicates that installing a traffic control signal will improve the overall safety and/or operation of the intersection.
A traffic control signal should not be installed if it will seriously disrupt progressive traffic flow.
The study should consider the effects of the right-turn vehicles from the minor-street approaches. Engineering judgment should be used to determine what, if any, portion of the right-turn traffic is subtracted from the minor-street traffic count when evaluating the count against the above signal warrants.
Engineering judgment should also be used in applying various traffic signal warrants to cases where approaches consist of one lane plus one left-turn or right-turn lane. The site-specific traffic characteristics dictate whether an approach should be considered as one lane or two lanes. For example, for an approach with one lane for through and right-turning traffic plus a left-turn lane, engineering judgment could indicate that it should be considered a one-lane approach if the traffic using the left-turn lane is minor. In such a case, the total traffic volume approaching the intersection should be applied against the signal warrants as a one-lane approach. The approach should be considered two lanes if approximately half of the traffic on the approach turns left and the left-turn lane is of sufficient length to accommodate all left-turn vehicles.
Similar engineering judgment and rationale should be applied to a street approach with one lane plus a right-turn lane. In this case, the degree of conflict of minor-street right-turn traffic with traffic on the major street should be considered. Thus, right-turn traffic should not be included in the minor-street volume if the movement enters the major street with minimal conflict. The approach should be evaluated as a one-lane approach with only the traffic volume in the through/left-turn lane considered.
At a location that is under development or construction and where it is not possible to obtain a traffic count that would represent future traffic conditions, hourly volumes should be estimated as part of an engineering study for comparison with traffic signal warrants. Except for locations where the engineering study uses the satisfaction of Warrant 8 to justify a signal, a traffic control signal installed under projected conditions should have an engineering study done within 1 year of putting the signal into stop-and-go operation to determine if the signal is justified. If not justified, the signal should be taken out of stop-and-go operation or removed.
For signal warrant analysis, a location with a wide median, even if the median width is greater than 9 m (30 ft), should be considered as one intersection.
Option:
At an intersection with a high volume of left-turn traffic from
the major street, the signal warrant analysis may be performed in
a manner that considers the higher of the major-street left-turn
volumes as the “minor-street” volume and the corresponding
single direction of opposing traffic on the major street as the
“major-street” volume.
For signal warrant analysis, bicyclists may be counted as either vehicles or pedestrians.
Support:
When performing a signal warrant analysis, bicyclists riding in
the street with other vehicular traffic are usually counted as vehicles
and bicyclists who are clearly using pedestrian facilities are usually
counted as pedestrians.
Option:
Engineering study data may include the following:
- The number of vehicles entering the intersection in each hour from each approach during 12 hours of an average day. It is desirable that the hours selected contain the greatest percentage of the 24-hour traffic volume.
- Vehicular volumes for each traffic movement from each approach, classified by vehicle type (heavy trucks, passenger cars and light trucks, public-transit vehicles, and, in some locations, bicycles), during each 15-minute period of the 2 hours in the morning and 2 hours in the afternoon during which total traffic entering the intersection is greatest.
- Pedestrian volume counts on each crosswalk during the same periods as the vehicular counts in Item B above and during hours of highest pedestrian volume. Where young, elderly, and/or persons with physical or visual disabilities need special consideration, the pedestrians and their crossing times may be classified by general observation.
- Information about nearby facilities and activity centers that serve the young, elderly, and/or persons with disabilities, including requests from persons with disabilities for accessible crossing improvements at the location under study. These persons might not be adequately reflected in the pedestrian volume count if the absence of a signal restrains their mobility.
- The posted or statutory speed limit or the 85th-percentile speed on the uncontrolled approaches to the location.
- A condition diagram showing details of the physical layout, including such features as intersection geometrics, channelization, grades, sight-distance restrictions, transit stops and routes, parking conditions, pavement markings, roadway lighting, driveways, nearby railroad crossings, distance to nearest traffic control signals, utility poles and fixtures, and adjacent land use.
- A collision diagram showing crash experience by type, location, direction of movement, severity, weather, time of day, date, and day of week for at least 1 year.
The following data, which are desirable for a more precise understanding of the operation of the intersection, may be obtained during the periods specified in Item B of the preceding paragraph:
- Vehicle-hours of stopped time delay determined separately for each approach.
- The number and distribution of acceptable gaps in vehicular traffic on the major street for entrance from the minor street.
- The posted or statutory speed limit or the 85th-percentile speed on controlled approaches at a point near to the intersection but unaffected by the control.
- Pedestrian delay time for at least two 30-minute peak pedestrian delay periods of an average weekday or like periods of a Saturday or Sunday.
- Queue length on stop-controlled approaches.
Section 4C.02 Warrant 1, Eight-Hour Vehicular Volume
Support:
The Minimum Vehicular Volume, Condition A, is intended for application
at locations where a large volume of intersecting traffic is the
principal reason to consider installing a traffic control signal.
The Interruption of Continuous Traffic, Condition B, is intended for application at locations where Condition A is not satisfied and where the traffic volume on a major street is so heavy that traffic on a minor intersecting street suffers excessive delay or conflict in entering or crossing the major street.
It is intended that Warrant 1 be treated as a single warrant. If Condition A is satisfied, then the criteria for Warrant 1 is satisfied and Condition B and the combination of Conditions A and B are not needed. Similarly, if Condition B is satisfied, then the criteria for Warrant 1 is satisfied and the combination of Conditions A and B is not needed.
Standard:
The need for a traffic control signal shall be considered if an
engineering study finds that one of the following conditions exist
for each of any 8 hours of an average day:
- The vehicles per hour given in both of the 100 percent columns of Condition A in Table 4C-1 exist on the major-street and the higher-volume minor-street approaches, respectively, to the intersection; or
- The vehicles per hour given in both of the 100 percent columns of Condition B in Table 4C-1 exist on the major-street and the higher-volume minor-street approaches, respectively, to the intersection.
In applying each condition the major-street and minor-street volumes shall be for the same 8 hours. On the minor street, the higher volume shall not be required to be on the same approach during each of these 8 hours.
| Condition A—Minimum Vehicular Volume | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Number
of lanes for moving traffic on each approach |
Vehicles
per hour on major street (total of both approaches) |
Vehicles
per hour on higher-volume minor-street approach (one direction only) |
|||||||
| Major Street | Minor Street | 100%a | 80%b | 70%c | 56%d | 100%a | 80%b | 70%c | 56%d |
| 1................. | 1................. | 500 | 400 | 350 | 280 | 150 | 120 | 105 | 84 |
| 2 or more..... | 1................. | 600 | 480 | 420 | 336 | 150 | 120 | 105 | 84 |
| 2 or more..... | 2 or more..... | 600 | 480 | 420 | 336 | 200 | 160 | 140 | 112 |
| 1................. | 2 or more..... | 500 | 400 | 350 | 280 | 200 | 160 | 140 | 112 |
| Condition B—Interruption of Continuous Traffic | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Number
of lanes for moving traffic on each approach |
Vehicles
per hour on major street (total of both approaches) |
Vehicles
per hour on higher-volume minor-street approach (one direction only) |
|||||||
| Major Street | Minor Street | 100%a | 80%b | 70%c | 56%d | 100%a | 80%b | 70%c | 56%d |
| 1................. | 1................. | 750 | 600 | 525 | 420 | 75 | 60 | 53 | 42 |
| 2 or more..... | 1................. | 900 | 720 | 630 | 504 | 75 | 60 | 53 | 42 |
| 2 or more..... | 2 or more..... | 900 | 720 | 630 | 504 | 100 | 80 | 70 | 56 |
| 1................. | 2 or more..... | 750 | 600 | 525 | 420 | 100 | 80 | 70 | 56 |
a Basic minimum hourly volume.
b Used for combination of Conditions
A and B after adequate trial of other remedial measures.
c May be used when the major-street
speed exceeds 70 km/h or exceeds 40 mph or in an isolated community
with a population of less than 10,000.
d May be used for combination of
Conditions A and B after adequate trial of other remedial measures
when the major-street speed exceeds 70 km/h or exceeds 40 mph or
in an isolated community with a population of less than 10,000.
Option:
If the posted or statutory speed limit or the 85th-percentile speed
on the major street exceeds 70 km/h or exceeds 40 mph, or if the
intersection lies within the built-up area of an isolated community
having a population of less than 10,000, the traffic volumes in
the 70 percent columns in Table 4C-1 may be used in place of the
100 percent columns.
Guidance:
The combination of Conditions A and B is intended for application
at locations where Condition A is not satisfied and Condition B
is not satisfied and should be applied only after an adequate trial
of other alternatives that could cause less delay and inconvenience
to traffic has failed to solve the traffic problems.
Standard:
The need for a traffic control signal shall be considered if an
engineering study finds that both of the following conditions exist
for each of any 8 hours of an average day:
- The vehicles per hour given in both of the 80 percent columns of Condition A in Table 4C-1 exist on the major-street and the higher-volume minor-street approaches, respectively, to the intersection; and
- The vehicles per hour given in both of the 80 percent columns of Condition B in Table 4C-1 exist on the major-street and the higher-volume minor-street approaches, respectively, to the intersection.
These major-street and minor-street volumes shall be for the same 8 hours for each condition; however, the 8 hours satisfied in Condition A shall not be required to be the same 8 hours satisfied in Condition B. On the minor street, the higher volume shall not be required to be on the same approach during each of the 8 hours.
Option:
If the posted or statutory speed limit or the 85th-percentile speed
on the major street exceeds 70 km/h or exceeds 40 mph, or if the
intersection lies within the built-up area of an isolated community
having a population of less than 10,000, the traffic volumes in
the 56 percent columns in Table 4C-1 may be used in place of the
80 percent columns.
Section 4C.03 Warrant 2, Four-Hour Vehicular Volume
Support:
The Four-Hour Vehicular Volume signal warrant conditions are intended
to be applied where the volume of intersecting traffic is the principal
reason to consider installing a traffic control signal.
Standard:
The need for a traffic control signal shall be considered if an
engineering study finds that, for each of any 4 hours of an average
day, the plotted points representing the vehicles per hour on the
major street (total of both approaches) and the corresponding vehicles
per hour on the higher-volume minor-street approach (one direction
only) all fall above the applicable curve in Figure 4C-1 for the
existing combination of approach lanes. On the minor street, the
higher volume shall not be required to be on the same approach during
each of these 4 hours.
Option:
If the posted or statutory speed limit or the 85th-percentile speed
on the major street exceeds 70 km/h or exceeds 40 mph or if the
intersection lies within the built-up area of an isolated community
having a population of less than 10,000, Figure 4C-2 may be used
in place of Figure 4C-1.
Figure 4C-1 Warrant 2, Four-Hour Vehicular Volume
Figure 4C-2 Warrant 2, Four-Hour Vehicular Volume (70% Factor)
Section 4C.04 Warrant 3, Peak Hour
Support:
The Peak Hour signal warrant is intended for use at a location where
traffic conditions are such that for a minimum of 1 hour of an average
day, the minor-street traffic suffers undue delay when entering
or crossing the major street.
Standard:
This signal warrant shall be applied only in unusual cases, such
as office complexes, manufacturing plants, industrial complexes,
or high-occupancy vehicle facilities that attract or discharge large
numbers of vehicles over a short time.
The need for a traffic control signal shall be considered if an engineering study finds that the criteria in either of the following two categories are met:
- If all three of the following conditions exist for the same
1 hour (any four consecutive 15-minute periods) of an average
day:
- The total stopped time delay experienced by the traffic on one minor-street approach (one direction only) controlled by a STOP sign equals or exceeds: 4 vehicle-hours for a one-lane approach; or 5 vehicle-hours for a two-lane approach, and
- The volume on the same minor-street approach (one direction only) equals or exceeds 100 vehicles per hour for one moving lane of traffic or 150 vehicles per hour for two moving lanes, and
- The total entering volume serviced during the hour equals or exceeds 650 vehicles per hour for intersections with three approaches or 800 vehicles per hour for intersections with four or more approaches.
- The plotted point representing the vehicles per hour on the major street (total of both approaches) and the corresponding vehicles per hour on the higher-volume minor-street approach (one direction only) for 1 hour (any four consecutive 15-minute periods) of an average day falls above the applicable curve in Figure 4C-3 for the existing combination of approach lanes.
Option:
If the posted or statutory speed limit or the 85th-percentile speed
on the major street exceeds 70 km/h or exceeds 40 mph, or if the
intersection lies within the built-up area of an isolated community
having a population of less than 10,000, Figure 4C-4 may be used
in place of Figure 4C-3 to satisfy the criteria in the second category
of the Standard.
Figure 4C-3 Warrant 3, Peak Hour
Figure 4C-4 Warrant 3, Peak Hour (70% Factor)
Section 4C.05 Warrant 4, Pedestrian Volume
Support:
The Pedestrian Volume signal warrant is intended for application
where the traffic volume on a major street is so heavy that pedestrians
experience excessive delay in crossing the major street.
Standard:
The need for a traffic control signal at an intersection or midblock
crossing shall be considered if an engineering study finds that
both of the following criteria are met:
- The pedestrian volume crossing the major street at an intersection or midblock location during an average day is 100 or more for each of any 4 hours or 190 or more during any 1 hour; and
- There are fewer than 60 gaps per hour in the traffic stream of adequate length to allow pedestrians to cross during the same period when the pedestrian volume criterion is satisfied. Where there is a divided street having a median of sufficient width for pedestrians to wait, the requirement applies separately to each direction of vehicular traffic.
The Pedestrian Volume signal warrant shall not be applied at locations where the distance to the nearest traffic control signal along the major street is less than 90 m (300 ft), unless the proposed traffic control signal will not restrict the progressive movement of traffic.
If this warrant is met and a traffic control signal is justified by an engineering study, the traffic control signal shall be equipped with pedestrian signal heads conforming to requirements set forth in Chapter 4E.
Guidance:
If this warrant is met and a traffic control signal is justified
by an engineering study, then:
- If at an intersection, the traffic control signal should be traffic-actuated and should include pedestrian detectors.
- If at a nonintersection crossing, the traffic control signal should be pedestrian-actuated, parking and other sight obstructions should be prohibited for at least 30 m (100 ft) in advance of and at least 6.1 m (20 ft) beyond the crosswalk, and the installation should include suitable standard signs and pavement markings.
- Furthermore, if installed within a signal system, the traffic control signal should be coordinated.
Option:
The criterion for the pedestrian volume crossing the major roadway
may be reduced as much as 50 percent if the average crossing speed
of pedestrians is less than 1.2 m/sec (4 ft/sec).
A traffic control signal may not be needed at the study location if adjacent coordinated traffic control signals consistently provide gaps of adequate length for pedestrians to cross the street, even if the rate of gap occurrence is less than one per minute.
Section 4C.06 Warrant 5, School Crossing
Support:
The School Crossing signal warrant is intended for application where
the fact that school children cross the major street is the principal
reason to consider installing a traffic control signal.
Standard:
The need for a traffic control signal shall be considered when an
engineering study of the frequency and adequacy of gaps in the vehicular
traffic stream as related to the number and size of groups of school
children at an established school crossing across the major street
shows that the number of adequate gaps in the traffic stream during
the period when the children are using the crossing is less than
the number of minutes in the same period (see Section
7A.03) and there are a minimum of 20 students during the highest
crossing hour.
Before a decision is made to install a traffic control signal, consideration shall be given to the implementation of other remedial measures, such as warning signs and flashers, school speed zones, school crossing guards, or a grade-separated crossing.
The School Crossing signal warrant shall not be applied at locations where the distance to the nearest traffic control signal along the major street is less than 90 m (300 ft), unless the proposed traffic control signal will not restrict the progressive movement of traffic.
Guidance:
If this warrant is met and a traffic control signal is justified
by an engineering study, then:
- If at an intersection, the traffic control signal should be traffic-actuated and should include pedestrian detectors.
- If at a nonintersection crossing, the traffic control signal should be pedestrian-actuated, parking and other sight obstructions should be prohibited for at least 30 m (100 ft) in advance of and at least 6.1 m (20 ft) beyond the crosswalk, and the installation should include suitable standard signs and pavement markings.
- Furthermore, if installed within a signal system, the traffic control signal should be coordinated.
Section 4C.07 Warrant 6, Coordinated Signal System
Support:
Progressive movement in a coordinated signal system sometimes necessitates
installing traffic control signals at intersections where they would
not otherwise be needed in order to maintain proper platooning of
vehicles.
Standard:
The need for a traffic control signal shall be considered if an
engineering study finds that one of the following criteria is met:
- On a one-way street or a street that has traffic predominantly in one direction, the adjacent traffic control signals are so far apart that they do not provide the necessary degree of vehicular platooning.
- On a two-way street, adjacent traffic control signals do not provide the necessary degree of platooning and the proposed and adjacent traffic control signals will collectively provide a progressive operation.
Guidance:
The Coordinated Signal System signal warrant should not be applied
where the resultant spacing of traffic control signals would be
less than 300 m (1,000 ft).
Section 4C.08 Warrant 7, Crash Experience
Support:
The Crash Experience signal warrant conditions are intended for
application where the severity and frequency of crashes are the
principal reasons to consider installing a traffic control signal.
Standard:
The need for a traffic control signal shall be considered
if an engineering study finds that all of the following criteria
are met:
- Adequate trial of alternatives with satisfactory observance and enforcement has failed to reduce the crash frequency; and
- Five or more reported crashes, of types susceptible to correction by a traffic control signal, have occurred within a 12-month period, each crash involving personal injury or property damage apparently exceeding the applicable requirements for a reportable crash; and
- For each of any 8 hours of an average day, the vehicles per hour (vph) given in both of the 80 percent columns of Condition A in Table 4C-1 (see Section 4C.02), or the vph in both of the 80 percent columns of Condition B in Table 4C-1 exists on the major-street and the higher-volume minor-street approach, respectively, to the intersection, or the volume of pedestrian traffic is not less than 80 percent of the requirements specified in the Pedestrian Volume warrant. These major-street and minor-street volumes shall be for the same 8 hours. On the minor street, the higher volume shall not be required to be on the same approach during each of the 8 hours.
Option:
If the posted or statutory speed limit or the 85th-percentile
speed on the major street exceeds 70 km/h or exceeds 40 mph, or
if the intersection lies within the built-up area of an isolated
community having a population of less than 10,000, the traffic volumes
in the 56 percent columns in Table 4C-1 may be used in place of
the 80 percent columns.
Section 4C.09 Warrant 8, Roadway Network
Support:
Installing a traffic control signal at some intersections might
be justified to encourage concentration and organization of traffic
flow on a roadway network.
Standard:
The need for a traffic control signal shall be considered if an
engineering study finds that the common intersection of two or more
major routes meets one or both of the following criteria:
- The intersection has a total existing, or immediately projected, entering volume of at least 1,000 vehicles per hour during the peak hour of a typical weekday and has 5-year projected traffic volumes, based on an engineering study, that meet one or more of Warrants 1, 2, and 3 during an average weekday; or
- The intersection has a total existing or immediately projected entering volume of at least 1,000 vehicles per hour for each of any 5 hours of a nonnormal business day (Saturday or Sunday).
A major route as used in this signal warrant shall have one or more of the following characteristics:
- It is part of the street or highway system that serves as the principal roadway network for through traffic flow; or
- It includes rural or suburban highways outside, entering, or traversing a City; or
- It appears as a major route on an official plan, such as a major street plan in an urban area traffic and transportation study.
