This FHWA guide on HOT lane development was prepared in 2003 and is intended to be a comprehensive source of collected experience gained from the nation's current and implemented high-occupancy toll (HOT) lane projects. The guide presents a wide range of information on HOT lanes and can be used to assist transportation professionals contemplating specific projects. The relatively new concept of HOT lanes may be a promising option for transportation officials to manage highway congestion. HOT lanes are a highway demand management strategy that seeks to increase efficiency and throughput on existing highways by combining High Occupancy Vehicle (HOV) lanes and pricing strategies by allowing single occupancy vehicles to gain access to HOV lanes by paying a toll. The lanes are "managed" through pricing to maintain free flow conditions even during periods of peek demand. HOT lanes can thus increase the use of HOV lanes by allowing willing users to pay a premium in exchange for more reliable travel time and generate additional revenue. HOT lanes often utilize sophisticated electronic toll collection and traffic information systems. Information on price levels and travel conditions is normally communicated to motorists via variable message signs.
In order to maximize the efficiency of HOT lanes, increase travel time savings and attract paying users, HOT lanes must provide premium travel conditions and predictable trip times. Operators vary HOT toll prices and vehicle occupancy requirements to limit volumes and ensure reliable speed advantages when adjacent general-purpose lanes are congested. During periods of peak demand, determined by either time-of-day as with the SR 91, or on a real-time basis based on congestion levels as with the I-15, toll prices are thus raised to maintain premium conditions.
Setting an optimal toll price in conjunction with occupancy requirements is a difficult task. It requires initial travel demand modeling and forecasting for HOT lanes and non-HOT parallel lanes as well as daily lane management based on traffic volumes. Traffic forecasting in turn requires gathering data and making assumption about trip origins and destinations, vehicle occupancies, and alternative transportation routes and modes. The demand elasticity or the sensitivity of travelers' willingness to use the HOT lane with respect to changes in variables such as price, income, congestion, and trip purpose, must also be estimated. However, road conditions and traveler preferences can vary over time and across geographic areas.
Several steps can be taken in order to establish more efficient prices and vehicle occupancy requirements:
- Determine the travel time savings differential for HOT lanes. At the minimum, demand assessments must consider the amount of travel time that HOT lanes save relative to non-HOT lanes and estimate the value of that travel time. A safe assumption is that motorists will be attracted to the HOT lanes if out-of-pocket costs are smaller than the value of time savings. The value of travel time savings during a given time of day or for a given level of congestion can thus serve as a ceiling toll price.
- Conduct behavioral surveys and stated preference surveys to determine motorists' willingness to pay for use of HOT lanes. Forecasting traveler behavior is difficult and is often limited by lack of data. One option is to directly ask drivers their route and lane choices under different price and congestion scenarios. Such surveys can determine potential HOT market share of total travel in an area and provide guidance for pricing and occupancy requirements. Motorists can for example be asked directly if they would consider carpooling to take advantage of HOT lanes.
- CPTC, the private company that implemented and operates SR 91 HOT lanes in Orange County, combined public outreach with surveys on projected usage and willingness to pay for use of the lanes.
- Perform sensitivity analysis to show likely range in revenue and utilization figures. Sensitivity analysis should be performed to determine the possible range of paying and free access vehicles that may utilize the HOT facility. For example, an evaluation study of State Route 13 in Los Angeles County, CA showed that raising vehicle occupancy requirements from two to three increased the number of toll paying vehicles using the HOT lane. Raising the toll from ten cents to twenty cents a mile reduced overall demand, but increased the demand for high occupancy vehicles.
- Make conservative assumptions regarding travel demand characteristics. Experience with toll roads and transit systems indicate a tendency for demand projections and revenue forecasts to err on the high side.
- Calibrate pricing hierarchies and vehicle occupancy restrictions once facilities become operational in order to achieve the desired result. Monitor traffic volumes and adjust prices over time accordingly. Whether the overall goal is to maximize revenue or to maximize travel time savings, toll prices and other restrictions should be set to avoid either congestion or under-utilization on the HOT lane.
Houston's Katy Freeway QuickRide lane began as an HOV lane. Vehicle occupancy restrictions were gradually eased from buses and vanpools to registered carpools of four or more, then three or more and finally two or more. With HOV 2+ requirements, the HOV lane became congested during peak periods. However, when HOV 3+ requirements where reinstated, traffic declined by 30 percent and the lane became under-utilized. In 1998, it was converted to an HOT facility, where vehicles with two occupants now pay a two-dollar toll depending on the time of day and those with three or more occupants have free access. This mix of pricing and vehicle restrictions achieved optimal utilization of the restricted lane.
The SR 91 began as a flat toll facility. Tolls were then varied hour-by-hour during the morning and evening rush hours. HOV 3+ vehicles also began paying fifty percent of the toll price in 1998 in order to maintain free flow conditions. In addition to hour-by-hour adjustments, tolls have also been structured to reflect seasonal periods and trends in travel demand.
- Price lanes to achieve throughput below the maximum level. HOT lanes should be managed with the aim of providing premium "free flow" conditions. Maximum throughput however is often achieved at lower speeds. HOT lanes instead should offer higher speeds at the expense of lower throughput. In order to provide such premiums service, traffic volumes and speeds must be constantly monitored. Prices should either respond in real-time or time-of-day prices should be revised regularly to match changes in speed and volume. Houston's I-10 Katy Freeway QuickRide manages its one lane facility at 1500 vehicles/hour, while the SR 91 Express Lanes operates a two lane facility with flow rates of 1800 vehicles/hour/lane. HOT lane operators should use prices and vehicle occupancy restrictions to aim for an average of 1700 automobile equivalents per lane with the understanding that road configurations, slopes and speed limits can drive this number up or down. In addition to pricing and vehicle occupancy requirements, access and eligibility restrictions can be used to manage lanes and maintain free flow conditions.
Pricing, vehicle occupancy requirements and other lane management tools are critical for successful HOT lane performance. The operator must have a fundamental understanding of the effect of day-to-day traffic changes and long-term demographic changes on HOT utilization. The ability to manage and price a HOT lane requires an ongoing monitoring presence and the ability to aggressively react to conditions that affect roadway performance. Only then can an HOT lane meet its objectives in commute periods when it is most needed and justified. Effectively managing and pricing HOT lanes to optimize the roadway performance addresses the ITS goals of mobility, efficiency, and customer satisfaction.
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