Many decision points exist while approaching the plaza, at the plaza, and on departure from the plaza. The decision points can lead to vehicle merging, weaving, queuing, diverging and differential speeds. Diverging and weaving occurs on the approach to the plaza as electronic toll collection (ETC) users separate from cash paying customers, who then further diverge based on selected cash payment lane type, shortest traffic queue, and lane status (i.e., open or closed). Multiple collection methods can increase the potential for side swipe and rear-end collisions if the lane groupings are not clear to users who are making choices of which lane to use for payment. Potential safety hazards particularly exist when approaching and departing ETC dedicated lanes. When an driver unfamiliar with the toll plaza realizes their vehicle is in the wrong payment lane and suddenly stops, a following high-speed, ETC–equipped vehicle can easily collide with the stopped vehicle. Consequently, speed variance is another important factor to be considered at mixed use toll facilities. Similarly, merging and weaving occurs on the departure side of the plaza as the number of toll lanes tapers down to the width of the continuing mainline.
Various studies and reports have presented summaries of the state-of-the-practice within the industry, primarily related to specific design elements or practices of toll agencies. The present environment is seeing significant increases in new toll highway miles, resulting in more toll plazas, most of which include high speed express lanes for ETC users only. Further trends show toll roads facing greater commuter and recreational demands, resulting in cash paying and ETC users familiar with the toll road mixed with unfamiliar cash paying users. Without the use of good design practice, including effective deployment of various traffic control devices, this mix can result in unsafe and inefficient operations. ETC users now expect non-stop, high speed travel through toll plazas without incurring any delays. Development of national guidelines that address the implications of electronic toll collection on plaza operations has therefore become much more critical.
Toll plazas have been designed and constructed in the United States without the benefit of national toll plaza design guidelines and standards, often resulting in driver unfamiliarity and inefficient vehicle throughput. Without national guidelines and standards, designs have evolved placing undue focus on monetary constraints, deploying signs with too little or too much information, inefficiently configuring toll lanes and embodying design features with greater emphasis on establishing a unique identity than on plaza safety and operations. As a result, toll plaza design elements and practices vary from agency to agency, and are often dictated by either legacy toll plaza design practices or variations to historical designs that retains a distinctive appearance while incorporating enhancements to correct deficiencies. Plaza modifications made to add electronic toll collection (ETC) to existing plaza facilities also vary by agency. In further complicating operations and adding driver confusion, some agencies have enacted variable pricing schemes to reduce plaza delays by shifting travel demand.
Improvements and modifications to existing plazas are impacted by right-of-way constraints, requirements for maintenance of traffic and revenue, provisions for future improvements and budget considerations. Few agencies can afford to construct entirely new toll plazas that incorporate design features to maximize safety and efficient plaza operations. Incremental changes, however, may lack sufficient design analyses and incorporate minimum design elements needed for safe and efficient operations. Increases in plaza collisions and operational performance deficiencies often result from these incremental changes.
In contrast to traditional public highway departments and agencies when considering the application of traffic control devices, a toll agency has to follow a different business-customer philosophy. In addition to the various legacy provisions and constraints described earlier, the agency must consider their customer base, and how they can equitably serve the various customer groups (i.e. short-trip/long-trip, commuter/recreational, etc). With the use of electronic toll collection technology, the manner that the toll agency markets and serves their customer base through its business rules and ETC fulfillment procedures will affect toll plaza operations. The degree of success in implementing this business-customer philosophy along with good engineering judgment will dictate the best application of various traffic control strategies and devices.
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