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22 Assessing the results is briefly described from a system standpoint and also from a traveler standpoint in the following sections. SYSTEM STANDPOINT Transportation management agencies often need to measure reliability performance levels of given transportation systems: the entire network, sub-area, or specific cor- ridor. The agencies can design and perform the simulation experiments to obtain the complete distribution of travel times the particular system could ever experience over different times of day and different days. The results (i.e., the overall travel time dis- tribution and the associated reliability measures) can be used to answer questions like the following: How dispersed are travel times on this system? What proportion of travelers experience serious congestion along this road? How unreliable or uncertain is the travel time on a given road compared with another road? ASSESSING TRAVEL TIME UNCERTAINTY DURING A PARTICULAR DEPARTURE TIME INTERVAL: TRAVELER STANDPOINT Transportation management agencies also need to be able to estimate and predict the reliability levels that individual travelers will experience so they can provide travelers with accurate travel information or warning messages. Agencies can obtain the travel time distribution for a particular departure time interval to assess the probability that a particular traveler departing at that interval will experience a specific level of conges- tion. Another important user-level measure is the schedule delay experienced, which is the difference between the actual and the desired arrival time for that individual. 6 ASSESSING THE RESULTS
