July 18, 1998

DYNAMIC PRICING:San Diego’s I-15 goes smoothly but may be more aggressively priced

Originally published in issue 29 of Tollroads Newsletter, which came out in Jul 1998.


Subjects:dynamic congestion pricing

Facilities:CA/I-15 HOT I-15


Locations:San Diego CA

Sources:Kim Kawada

Dynamic road pricing works, motorists accept it, and signs are the project will be a big success. As intended the pricing, or toll buy-in by electronic transponder, has increased utilization of the express lanes and reduced the waste inherent in HOV operation. The dynamic pricing is successfully metering toll-SOV entry to maintain free flow conditions.

Most likely change by managers will be an increase in traffic numbers for each ‘level of service’ definition and toll rate.

The project is something of a technical triumph for TransCore which has been in charge of the programming and systems integration. It also vindicates the San Diego officials who brushed aside last minute doubts expressed by Wilbur Smith and other consultants who suggested a fixed stepped time schedule of charges like 91-Express.

“We’ve resolved all the technical problems and it seems to be going very smoothly,” says Sarah Lawrence, transp specialist at the San Diego Association of Governments (SANDAG), which is conducting the project with funding from the Federal Highway Admin. Lawrence says that the maximum toll rates set have proven high enough for the dynamic tolling to operate freely most of the time. The toll rate caps are being hit occasionally but usually only for one or two of the 6-minute intervals between toll rate adjustments. On Friday evenings northbound there have been times when the level of traffic kept the tolls at the max rate of $4/trip for 3 or more intervals — 18 mins.

Lawrence says that they are carefully watching the Friday afternoon situation and may press for revisions to the caps.

The HOT lanes are running about 12k vehs/day currently over the 7.5hrs they are in operation so they can carry a lot more vehicles (2x7.5x1500) 22k would probably be the maximum if Level of Service C was to be maintained. Kim Kawada, the project manager explains that SANDAG and Caltrans have been very conservative in setting their definition of traffic volumes and associated Level of Service. They are using 1300 veh/hr/lane rather than the 1584 of the Highway Capacity Manual as their definition of the volume that produces LOS-C. This is partly because of a choke point in the system toward the southern end where there is a fork southbound to CA-163 and I-15.

Kawada says that traffic is now seasonally light and that come the end of the summer they can expect a major seasonal increase. Vacations end and colleges go back. That could test the caps.

Toll/HOV split

Of the 12k veh/daily in the HOT lanes a bit over 1,600 are toll payers and over 10k (86%) are HOVs traveling free. In Oct 96, before the project began, traffic in the lanes was 9.5k veh/day so there has been an increase in carpooling as well as the addition of the tollpayers. The first batch of 5,000 transponders SANDAG ordered have now been issued, and a small waiting list is developing. More will probably be ordered, but they are not pushing recruitment at all. There is no active marketing because they don’t want a surge of users. Several percent of toll patrons are motorists with transponders from TCA or 91-Express in Orange Co to the north.

Lawrence and Kawada say there are some complaints from motorists that the system is not allowing enough toll payers in. They say there have been some complaints from people paying the maximum toll rate and still being able to travel through at 70mph (110km/hr) or more. They think it should be busier before the system pushes the toll to the max. Kawada says they will be discussing with Caltrans the possibility of moving up the volume definition of LOS-C which they are expected to sustain — closer to the Highway capacity Manual number of 1584 veh/lane/hr. That would allow more vehicles into the lanes at generally lower tolls and also give them more flexibility at the peak of the peak.


Violators are running less than 3% to 4% of the total, a bit lower than when it was a HOV lane. They have no enforcement camera system in place and have put on hold plans to install one in the toll lane. Most violators simply scream through the HOV lanes. For now enforcement is traditional random police cruiser ambush.


The I-15 congestion pricing pilot project is being conducted on a 13km (8mi) 2-lane reversible barriered HOV facility in the center of the I-15 freeway in the northern part of the San Diego metro area. The facility is open 3.5 hours southbound in the mornings and 4-hours northbound evenings. Under the congestion pricing program HOV-2s (vehicles with at least 2 occupants) continue to travel free as before. In two previous phases called ExpressPass, single occupant vehicles were able to buy a monthly pass for $50, later increased to $70, for unlimited trips. The maximum monthly passes in use was 967 and there was a long waiting list for passes at these prices. At first the pass consisted of a visually sighted windshield sticker, then toll transponders used purely in the automatic identification mode.

Since March 30 1998 per trip tolling has been introduced with dynamic pricing, the first of its kind in the world. The system is marketed under the name FasTrak, the brand name used for electronic tolling elsewhere in California. Near the mid-point of the facility it has been widened from 2-lanes to 3-lanes. Motorists who have a FasTrak e-toll tag are directed by signs to travel in the eastern lane where the toll system reader on an overhead gantry is able to read their account number by radio signal.

Traffic volumes are counted by two pairs of in-pavement loop detectors 2.4m apart in the HOV lanes plus a Schwartz Autosense laser vehicle detector and profiler mounted over the toll lane. Traffic volumes are computed for six minute intervals and a moving average of 2x6min volumes goes to a ‘look-up table’ of times and volume ranges and toll rates. There is a lag built in to ensure that a motorist is not charged more than the toll rate that was displayed on a variable message sign on the approaches to the toll lanes at the time that motorist made a decision to enter the toll express lanes rather than go free on the adjacent unrestricted lanes.


Motorists on I-15 think that higher tolls are a better way of combatting congestion on the express lanes than tougher vehicle occupant requirements. And they want tolls used for highway improvements and overwhelmingly oppose using toll revenues to subsidize transit. I-15 HOT lanes toll payers are heavily rich guys (household incomes over $100k)

Those are some of the conclusions of the first published survey of I-15 toll buy-in users characteristics and attitudes. Called the “Phase I Attitudinal Panel Study” (May 29, 1998) it was the first of a series of monitoring and assessment reports on the I-15 congestion pricing project for SANDAG and FHWA by San Diego State Univ Foundation. Project director is Janusz Supernak. Survey work was done by Jacqueline Golob and associates. 1,500 telephone surveys were done of I-15 users (both express lanes and regular lanes users) with a control group of users of I-8 a separate freeway in the area. The surveys cover the period when a $70 monthly fee was being charged for the right to travel solo in the HOV lanes.

The rich guys

Those concerned with ‘equity’ will latch onto the high income of those solo drivers buying into the HOV lanes in San Diego. 50% of ExpressPass users have household incomes over $100k compared to 20% of other I-15 users and 9% on I-8. 83% of those in the toll buy-in have incomes over $60k compared to 55% in the free lanes and 34% on I-8. On 91-Express by contrast surveys have shown relatively little difference in the incomes of toll-payers relative to others. That may be due to the fact that Riverside County where most CA-91 users reside is relatively low income. By contrast the northern part of San Diego county feeding I-15 is the highest income part of the metro area. It may also be that the flat rate monthly fee ($70) in effect at the time of this survey was a factor and that now the per-trip tolling is in effect, usage of the lanes will be less skewed to the rich.

They have rights too

Perhaps the best that counter will be to point out that the fly-for-a-fee service harms noone — it takes wasted underutilized HOV space and puts it into service — and that, although the rich use it most, 17% of its users are of moderate household income ($20k to $60k).

And heck what’s this silly socialist-egalitarian prejudice about giving the rich options anyway? The rich have the option to buy a Mercedes or a Crown Victoria, or first class air travel with their money, so why shouldn’t they have the right to buy a higher class of road service as well?

The rich may be the villains of Hollywood docudramas but by and large they are the more productive members of society, and it is plain vindictive and stupid to force them to waste their time in stop-&-go traffic. Another thought — now that it isn’t necessary to lay out the $70/month and it is possible to pay for use of the HOT lanes on a more discriminating trip by trip basis, the usage may become a bit less skewed to these rich guys. So watch for later surveys.


A clear majority of ExpressPass users are very satisfied (61%) or somewhat satisfied (19%) with the express lanes, whereas the majority of solo drivers (66%) are dissatisfied with conditions in the traffic conditions in their lanes. 89% of ExpressPass users (HOTters) consider the scheme a success and 33% of carpoolers in the HOV lanes. 39% of carpoolers sharing the lanes with the toll buy-in solo drivers have no opinion about whether the scheme is a success and 27% say it is a failure. A majority (56%) of carpoolers agree that solo drivers should be allowed in the carpool lanes for a fee but 44% would prefer to keep them to themselves. Only 5% of carpoolers think admission of solo toll payers has lengthened their journey time, and a similar number think it has actually reduced their time, though 87% say there has been “no impact.” Solo drivers who don’t use the HOT lanes are about equally split between support and opposition to the scheme according to one question. Asked whether the HOT scheme is fair to regular drivers, the regular drivers say it is by a 72/28 split. 90% of HOT lane users think it’s fair, not surprisingly.

Time savings

ExpressPass users on average say they save about 20mins using the express lanes. Only 20% think they save less than 12mins and 26% think they save 23mins to 30mins. These are absurdly exaggerated perceptions according to the Supernak team. They ran 5 days of measurements clocking times in the two roadways and actual time savings in the express lanes ranged between zero and 9mins with an average of 5mins.

The phenomenon of exaggerated perceptions of delay in traffic is wellknown. Perhaps time seems to pass more slowly in stop&go or creeping traffic. Another explanation given is that people think of the worst delays they suffer in congested traffic when asked about “average” time savings. Elsewhere, express lanes drivers on 91-Express also exaggerate the savings they get, though not by as much as the I-15 HOTters.

The ExpressPass patrons say they make use of the extra time by leaving home 15mins to 30mins later, and the survey team think that maybe the greater reliability of travel in the HOT lanes makes them comfortable about leaving home so much later.

Want revenues for more highway

Most interesting is the puny support for using toll revenues to improve transit service — usually the planners preference. SANDAG in fact is using the revenues of the I-15 HOT lane to fund a new express bus service in the lanes. Less than 2% of I-15 motorists overall approve of this — 3% of carpoolers, 6% of ExpressPass users and 1% of solo drivers in the free/congested lanes. 66% of solo drivers and 42% of HOTters want any revenues spent on improving or adding regular highway lanes, and 21% of solo drivers and 31% of HOTters want it spent on extra HOT lanes. Carpoolers have about the same preference split as HOTters.


The HOT lanes seem to have a major safety appeal over the unrestricted lanes. 69% of ExpressPass users and 46% of unrestricted lane user think the HOT lanes are “much safer.” And 90% of the HOTters, 84% of carpoolers and 80% of regular lane users think the HOT lanes are at least “safer.” Only 2% to 6% think of the express lanes as less safe. The lack of big trucks, the greater distance between vehicles and the smoother flow apparently heavily outweigh any perception of high speed meaning higher danger in the HOT lanes. (Contact Kim Kawada SANDAG 619 595 5300, Janusz Supernak SDSU 619 594 6378 www.sandag.cog.ca.us)

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