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Information about BrownstoneEssex

Published on March 19, 2008

Author: Umberto


Lessons from Southern California Congestion Pricing Experiments:  Lessons from Southern California Congestion Pricing Experiments David Brownstone University of California, Irvine (with Ken Small, Tom Golob, Arindam Ghosh, Jia Yan, Seiji Steimetz) SR 91 Toll Facility:  SR 91 Toll Facility Privately funded 4 lanes in 8 miles of median in congested link between Riverside and L.A. / Orange County. Complex fixed time-of-day and week pricing schedule designed to maximize profit (revenue). Current maximum toll is $8.25, but carpools get 50% discount. Connects to much longer carpool lanes on both sides of facility. SR 91 Problems:  SR 91 Problems Politically very unpopular since private owners enforced a “no compete” clause with the state highway agency to prevent widening the free lanes. Private owners sold at a loss to local transportation agency, which is now stuck with paying off construction bonds. I-15 HOT lanes:  I-15 HOT lanes Publicly-funded 2 reversible lanes where solo drivers can pay to use carpool lanes. Links northern inland San Diego county to central business district. Real-time congestion pricing designed to keep free-flow in HOT lanes. Toll changes at most every 6 minutes, current maximum about $4.00 Changeable message signs give at least 30 seconds notice of current toll charge. I 15 Popularity:  I 15 Popularity I 15 toll facility is politically popular. Revenues fund an express bus system that primarily serves domestic help for wealthy residents. I 15 corridor users are high-income (especially compared to SR91) I 15 toll facility being expanded 15 miles north. Toll Facility Commonalities:  Toll Facility Commonalities Both use radio transponders to collect tolls, which requires users to establish accounts. Bypass very congested links on typically long (30-40 minute) commutes. Maximum time savings is about 10 minutes. Use of toll facility is voluntary – there is a free alternative following exactly the same route. Questions:  Questions Are these facilities better than just letting all vehicles use the new lanes? Are the charges set optimally? Do these toll facilities reduce vehicle emissions? Do these toll facilities increase safety? Can the answers to these questions be generalized to other areas (Governor interested in converting all carpool lanes to HOT lanes) Speed-Flow Curve:  Speed-Flow Curve Relates speed to traffic flow (the number of cars per lane-hour) As speeds increase, flow increases until following distance starts to decrease below drivers’ safety margin. (tailgating is good for traffic flow!) Speed-flow curve is reverse C shaped. Slide11:  Note that Fmax = 1500-2000 cars per hour on a freeway lane Congestion:  Congestion Congestion occurs when enough vehicles enter the road so that each additional vehicle lowers the traffic flow. This happens at the lower side of the speed-flow curve. Optimal Congestion:  Optimal Congestion Occurs when the marginal benefit of reducing congestion = marginal cost of reducing congestion. Marginal cost is typically the cost of adding new road capacity = $5-10 million per lane-mile Therefore optimal congestion is greater than zero. Too Much Congestion?:  Too Much Congestion? Does private marginal benefit of reducing congestion = social marginal benefit? No – individuals do not account for the effect of their deciding to take a trip on other travelers’ trip times. Therefore there is too much congestion. Solution: Congestion Pricing:  Solution: Congestion Pricing Charge commuters entering congested roads an amount equal to value of time (VOT) lost to all other road users by their entering the road. This will depend on the VOT of all other road users, time and day, plus road conditions. When road is not congested, the optimal congestion toll is zero. Second Best Problems:  Second Best Problems When there is a free alternative, then optimal congestion toll is below VOT of other road users. Due to increased congestion on free alternative. Congestion Pricing Not Popular:  Congestion Pricing Not Popular Electricity – especially residential Telephones Disneyland Grocery and other retail stores Differences in VOT suggest a market for “premium” checkout lines Answers - Are these facilities better than just letting all vehicles use the new lanes?:  Answers - Are these facilities better than just letting all vehicles use the new lanes? Potentially yes since studies of commuters’ VOT on these corridors find considerable variation depending partially on income and length of trip. Are the charges set optimally?:  Are the charges set optimally? No, since both toll facilities set prices so that toll lanes are flowing freely. Recall that due to free alternative there should be some congestion in toll lanes! Setting optimal charges would be very hard to sell politically. Do these toll facilities reduce vehicle emissions? :  Do these toll facilities reduce vehicle emissions? Slight reduction (about 5%) relative to allowing free use of the toll lanes, but this is mostly due to setting tolls too high! There would be essentially no emission reductions with modern hybrid technology. If comparison is made to original system, then emissions are higher since toll facilities are new capacity! Do these toll facilities increase safety?:  Do these toll facilities increase safety? No, since free alternative is so congested that it is hard to get in a serious accident. The worst accidents are more frequent when road is near capacity. This suggests that congestion pricing may reduce safety, but not by a very large amount. Can the answers to these questions be generalized to other areas?:  Can the answers to these questions be generalized to other areas? Probably yes. Key VOT results are similar for both SR 91 and I 15 corridor in spite of large demographic differences and different survey modes (mail versus telephone). Model fit on I 15 data can accurately predict SR 91 results. How Should Revenue be Used?:  How Should Revenue be Used? Optimally should be used to reduce income taxes (reduces labor market distortions). Political feasibility seems to require recycling back to corridor users. I 15 bus service lowers cost of domestic help to same people paying tolls! Revenue will not be sufficient to build toll lanes. Value of time:  Value of time Marginal Benefit of reducing congestion is the value to road users of the time saved (VOT). For commercial users this is typically the value of time saved (wage) plus the inventory costs of goods delayed in transit. For work commute trips, VOT should be the opportunity cost of time = wage. But majority of freeway trips are not work trips or commercial trips. VOT for Commute Trips:  VOT for Commute Trips What is opportunity cost of commuting time? Work time? Home production? Leisure? VOT may not equal wage, and may vary across people and trips. VOT Variability:  VOT Variability Unless VOT varies across commuters, things like the 91 toll lanes cannot be efficient (because of free alternative). We would expect that VOT for work commute trips increases with wage, but perhaps not linearly. How to Measure Commute VOT:  How to Measure Commute VOT Revealed Preference – infer from commuter’s choices Mode Choice (bus, walk, bike, car) Route choice (especially toll vs. free) Stated Preference – ask commuter’s to respond to hypothetical experiments where they can pay to avoid congestion. Revealed Preference:  Revealed Preference Reflects actual choice behavior – but Very few situations where commuters can pay to reduce travel time – usually bundled with something else like carpooling Hard to measure time savings and cost for actual trips since there is a lot of variability in most commute trip times Stated Preference:  Stated Preference Example: Suppose you could pay $10 to reduce the time it took you to drive to school this morning by 10 minutes. Would you take this option? __Yes __No Worse alternative: How much would you pay to reduce your trip time by 10 minutes? Much cheaper than revealed preference studies. Stated Preference Problems:  Stated Preference Problems Respondent may not understand question, or may assume that the mechanism to reduce travel time is bundled with something else. Strategic Behavior: respondent may lie to influence public policy – they may overstate VOT to get more roads built This may explain urban rail results Results from LA HOT lane studies:  Results from LA HOT lane studies Revealed preference from SR91 and I15 HOT lanes finds VOT about $20/ hour of work commute trip time saved. Varies with income and trip distance Stated preference studies find VOT estimates about $10/ hour Identification Issues:  Identification Issues Use floating car to measure time savings. Assume commuters know distribution of time savings and toll level, but not actual time savings. SR91 variation in $/time saved from fixed toll schedule and carpool discount. I15 variation from HOT bypass ramp at key congested intersection. I15 HOT Lane Time Savings :  I15 HOT Lane Time Savings Slide35:            Slide36:      SP/RP differences:  SP/RP differences Difference persists across many different model specifications and very different SP collection methods (mail and CATI). Respondents are familiar with electronic toll collection and toll facilities. Respondents systematically perceive twice the actual time savings (more for women!). Safety:  Safety HOT choice bundled with perceived increased safety, and this might explain RP/SP differences Actually safer on regular lanes (due to slow speed) Steimetz (2004) models extra effort to avoid collisions in congested traffic, and finds this only accounts for 33% of RP/SP differences Value of Reliability:  Value of Reliability Commuters don’t like uncertain travel time. Cost of being late higher than being early, so measure uncertainty by 90th – 50th percentile of time savings distribution. Reliability is closely correlated with signaling function of real-time congestion tolls, so we can’t identify VOR from I15 data. Slide40:      VOR:  VOR VOT accounts for 2/3 and VOR 1/3 of the service quality differential between free and express lanes on SR91. Women have roughly twice the VOR as men, which explains why women more likely to take toll roads on both SR91 and I15.

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