Sunday before last, the Washington Post in its Sunday Metro section published a utopian depiction of VADOT’s proposed High Occupancy/Toll or HOT lane facility for I-95 in Northern Virginia. The artist’s rendition shows a vast multi-lane stretch of highway with six or eight free general purpose lanes flanking six HOT lanes in the median. Looks great! A commuter’s dream.
Unfortunately, however, the picture doesn’t tell the whole story, specifically the bottlenecks at the ends. All of those lanes must inevitably neck down to four or so either way to connect with the Washington Beltway on the north end and I-95 going south. In this regard VADOT’s grand depiction is somewhat dishonest.
During the critical commuting hours, those bottlenecks will cause traffic to back up. Result? Traffic congestion. VADOT is using the traffic congestion its own design causes as justification for building the HOT lane facility and for charging tolls for its use. They create the congestion and then present the HOT lanes as a quick way past it – for a price. Maryland’s MDOT is proposing to do exactly the same in its I-270 upgrade for Frederick County. In the current plan, the roadway will be widened to incorporate four Express Toll Lanes in the median between the free General Purpose lanes. The kicker is that the current four-lane design for the GP lanes and the congestion it produces will be retained for the new facility. Rather than fixing the congestion problem (by adding a free lane each way), MDOT is offering the Express Toll Lane facility as a way past the congestion – for a price. MDOT’s new design will be a virtual copy of the 91 Express Lanes tollway in Orange County, CA. This is a four-lane, 10-mile toll road built in the median of the Riverside Freeway (SR-91). It provides a good operating example for comparison with the ET lane design. One of the photographs on the 91 Express Lanes home page tells the whole story: nearly-deserted toll lanes on the left flanked by jammed free lanes on the right. I have used I-270 for more than thirty years as a commuter and as a casual user. Though I am now retired, I retain an engineering interest in I-270 and its problems. From my engineering point of view, the ET lane design will be extremely wasteful. The ET lanes are presented as a congestion-free way past I-270 congestion. To ensure free flow of traffic in the ET lanes, it will be necessary to cap traffic flow rate so as to restrict volume and minimize congestion. The currently-accepted nominal flow rate for HOV and ET lanes is 1600 vehicles per hour per lane. At 65 mph, the space used by each vehicle (5280 feet per mile times speed in miles per hour divided by flow rate) works out to 214.5 feet per vehicle, which leaves a lot of open space between vehicles (194.5 feet – about 10 car lengths). Put another way: that would be only 24.6 vehicles per mile. Set bumper-to-bumper, a lane can hold 264 vehicles per mile. The ET lanes will be almost deserted at their intended flow rate. The ET lanes will only be half used. In the morning, the lanes inbound toward DC will experience a traffic spike and the outbound lanes will be largely unused. In the afternoon, the reverse will occur. The net effect will be that two of the four lanes will be effectively unused and therefore superfluous. Most of the time, this very-expensive roadway will sit idle. This same usage pattern occurs daily on the Dulles Greenway running between Leesburg, VA, and Dulles Airport. Drive the Greenway at noon on a weekday and note how much traffic you see. Traffic flow rate will be controlled through toll structure. Toll structure controls flow rate by setting tolls higher during peak traffic hours to discourage casual use. A toll structure scheme is used by the 91 Express Lanes facility. Toll rates peak during the morning and afternoon commuting periods. Note that afternoon tolls are twice morning tolls. This could reflect greater demand in the afternoon or it could be simple price-gouging. Based on what we know, or can guess, we can estimate the annual toll income generated by the ET lanes. First, we need an estimate of traffic throughput. Let’s assume that all of the traffic flow in the ET lanes can be compressed into two 4-hour peak periods per day for a total of 8 hours per day. The rest of the day, I’m assuming the ET lanes will be unused. The traffic throughput will be 1600 vehicles per hour per lane times 8 hours per day times 2 lanes or 25,600 vehicles per day. Assuming further that the lanes will only be used on weekdays gives us 250 days per year and 6.4 million vehicles per year. Toll rates have probably not been determined, but let’s assume, for example, a nominal toll of $5 per vehicle (25 cents per mile). This would yield an estimated toll income of $32 million per year. Doubling the toll rate increases that to $64 million per year. MDOT might elect to split the tolls between morning and afternoon, that is, $5 in the morning and $10 in the afternoon, which would make annual toll income something like $50 million. For comparison, the California facility posted $43.3 million in user fees in 2009. Our simple estimates are therefore in the right ball park. Fifty million bucks would disappear into the State’s general fund without a ripple and would barely cover costs of operating and maintaining the ET lanes. The ET lanes will not fix existing congestion problems on I-270. They might make it possible for ET lane users to more quickly reach the congestion in Montgomery County caused by the HOV lanes there but won’t eliminate that congestion. They will enable afternoon commuters to bypass the bottleneck at MD121 but won’t fix that problem either. The ET lanes won’t be able to draw off enough traffic to ease congestion in the free lanes. The result of the $5-billion upgrade will be little or no improvement in traffic flow for the majority of I-270 users and a paltry return on investment from the ET lanes.