Estimating Toll Road Demand and Revenue (2007)

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49 All-or-nothing assignment—assignment approach in which all travel demand for each origin–destination pair is assigned to the shortest time path based on uncongested travel times. Barrier toll road—has one or more toll plazas that form a bar- rier across the roadway to prevent free passage. Motorists are required to pay a toll to continue, and the system usu- ally includes large mainline toll plazas and small toll plazas at on and off ramps. Closed barrier toll—a system that does not allow motorists to enter the roadway network without first paying a fee. Generally a payment or a ticket is issued at the entry and exit points in the roadway network. Electronic toll and traffic management (ETTM)—the use of two-way electronic communications between moving vehicles and roadside sensors for the purposes of toll col- lection and other traffic management functions. Electronic toll collection (ETC)—the use of automatic elec- tronic vehicle identification, such as transponders, for non- stop toll collection. Equilibrium assignment—a trip assignment algorithm that takes into account the build-up of volume and the ensu- ing changes in trip time when allocating trips to links. From the traveler’s perspective, the assignment simu- lates the driver’s desire to minimize overall his or her travel time (i.e., his or her travel costs) between a partic- ular origin and destination by switching paths. Equilib- rium occurs when the travel time on all possible paths for a given origin–destination is equal—that is, the driver no longer can improve his or her overall trip time by switch- ing paths. Equilibrium is achieved, usually after several iterations, when the difference in overall travel time (i.e., in generalized cost) summed over all trips and all origin– destination pairs is very small, between the current and previous iterations (i.e., is within specified absolute and/or percentage differences). Feed-back loops—part of the iterative modeling process where at the completion of the travel demand assign- ment, the resulting travel times or costs are fed back into trip generation, trip distribution, or mode split steps. The next iteration takes into account these travel costs for each origin–destination pair and recalculates the travel demand. Goodness of fit measures—used to validate models. Com- monly used measures include the following: Absolute comparison of the absolute difference between modeled flow and observed flow, on a given link or across a screenline. Relative comparison of difference between the modeled flow and the observed flow. That is, modeled flow divided by observed flow, with the comparison typically expressed as a percent. GEH statistic combines the absolute and relative com- parisons. It accounts for two types of error: that associ- ated with the simulated flow (reflecting the fit of the model) and that associated with the observed flow (through data collection errors and the day-to-day vari- ability of traffic). The statistic is defined as: The statistic is defined as: The GEH is properly a goodness of fit measure, rather than a statistical test. It is intended to give a quick indi- cation of how well the model is working. It can, and nor- mally is, applied to all model links for which observed counts are available. R2 is the correlation coefficient of the best-fit regression line of a plot of the modeled flows versus observed flows. This measure is commonly used to compare flows across a number of links, whether or not they are part of the same screenline or route (for example, all arterials in an urban network for which traffic counts are available). Correlation coefficients closer to 1.0 indicate a better goodness of fit. Open barrier toll—a system that allows motorists to enter the roadway network at certain locations without immediate payment prevents the motorist from proceeding past cer- tain points, unless a fee is paid. It can use electronic toll collection, which offers drivers the ability to pay tolls without stopping. Open road tolling—a system with no physical toll booths. All tolling is conducted by the identification of vehicles pass- ing under a gantry at each individual tolling point. Tolls are collected by one of two methods including electronic toll collection or video license plate identification system. Shadow toll—a payment and revenue process where instead of charging the user directly, businesses, land holders, or government agencies reimburse the private investor by accounting for the number and type of vehicles using the road, therefore allowing the private sector to invest the capital and the beneficiaries of the toll road to pay per the usage of the facility by the public. Stress test—used to assess the financial stability of a project (or of a portfolio of projects). The process reval- ues the project’s financial performance according to a different set of assumptions in the face; for example, of unforeseen “shocks.” Most asset markets lack a his- tory of returns that provide sufficient information about the behavior of markets under extreme events: stress tests complement traditional financial forecasting mod- els by testing how the project’s value changes in response to “exceptional but plausible” changes in the GEH observed flow simulated flow obs = − × ( ) . ( 2 0 5 erved flow simulated flow− ) GLOSSARY

underlying risk factors. In addition to testing “market risk” [such as toll revenues less than projected], the process also examines credit risk (losses from borrower defaults) and liquidity risks (illiquidity of assets and depositor runs). Several techniques have been developed in recent years. 50 Violation rate—a measure of the vehicles that are illegally evading the tolls compared with the number of vehicles using the tolled facility. Examples of toll evasion include, but are not limited to, the following: screening of license plates, using HOT lanes without the proper number of people, or using improper electronic pass with an unregistered vehicle.