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26 Synchronized phases sometimes get more green times Some of the operational features are listed for both because than necessary, creating unnecessary delay on the other they were handled well and/or not handled well by ATCSs. movements. This discrepancy in the reported observations can be attrib- System takes 5 to 10 s to respond to calls on minor uted to the knowledge that an ATCS of the same brand can phases--does not have detector switching. function differently based on how it was set up and custom- Single intersection falling off line. ized. There are also inherent differences in how various ATCS Poor split flexibility. brands handle certain operational conditions. From the list of System appears slower than expected when reacting to not-handled-well features one can observe several problems the variations of traffic flow and providing proper pro- that indicate poor fine-tuning or customization of ATCS gression on the corridor. parameters (e.g., delay on minor movements or ATCS per- Construction activity--the detectors are either torn up, formance on corridors under construction). These problems vehicles do not drive on them, or the lane is shut down do not necessarily indicate that the initial set up of the ATCS and the detector senses that it is broken and goes into a was poor, but that the system was not modified further, when "safe mode," causing problems. changes in operational conditions warranted such a modifi- Pedestrian traffic--the system theoretically handles cation. An agency needs to fully understand operations of its them well; however, our pedestrian volume is very high ATCS to recognize that the system needs modification, even and pedestrian phases are needed during most cycles. if the modification itself is done by an outside consultant. Because we compromised, a stage-type controller is used, which limits the ability of the operation to a dual- ring configuration; only 30% of the ATCS features are MAINTENANCE being used. Not possible to identify a camera failure unless the inter- ATCS users find that, in general, ATCS components are more section is monitored all the time. demanding with regard to maintenance than the comparable Data saving capacity--at present, data can be recalled components used by conventional traffic control systems. Fig- only for the previous seven days. ure 6 shows how ATCS users perceive maintenance of major Does not handle rush hour volumes well owing to pre- ATCS components (hardware, software, and communications). diction horizon being too close. Sixteen percent of the ATCS users find that maintenance is Emergency preemption and daily startup. much more demanding than with a regular system. Another Detection and communication failures. 44% of respondents agreed that maintenance of ATCS is Handling oversaturated traffic conditions. more demanding, but do not perceive such a large difference. Locked traffic flows--especially at roundabouts. Twenty-three percent found ATCSs to be similar to conven- Much less demanding than maintenance of Much more demanding regular traffic signals; 2; than maintenance of 5% regular traffic signals; 7; 16% Less demanding than maintenance of regular traffic signals; 5; 12% Same as maintenance of regular traffic signals; 10; 23% More demanding than maintenance of regular traffic signals; 19; 44% FIGURE 6 Level of difficulty of maintaining ATCSs.