Minnesota to do second toll express lanes - I-35W after I-394 success

December 9, 2007

Minnesota DOT is planning toll lanes on I-35W the major radial route heading south out of downtown Minneapolis two and a half years after successful introduction on I-394, the major western radial. The I-35W project has federal funding under the urban partnerships program but still needs to get the state match.

I-35W HOT lanes will go for 23km (14 miles) northbound and 19km (11.5 miles) southbound out of central Minneapolis. The portion closest in to downtown Minneapolis involves reconstruction of breakdown shoulders both sides of the roadway to full depth pavement (green in 3 color map).

The remainder involves adding tolling to HOV lanes already under construction (blue in 3 color map), and to existing HOV lanes (red in 3 color map).

Tolling will be required to be compatible with the I-394 MnPass toll systems which means the Raytheon-designed open standard ASTMv6 readers and transponders at the front end. Cofiroute, Wilbur Smith and local engineers SRF will have an inside running for the work, having developed experience at I-394 HOT lanes - generally judged to have produced a serious success story.

Costs of I-35W HOT lanes are expected to be around $30m for roadway improvements and $20m for ITS - sensors, toll systems, communications links and signage. It is a slightly more ambitious project than I-394 in scale and complexity.

Variable speeds in free lanes

An interesting part of the I-35W project is the use of variable speed limits in the three free lanes to the right of the HOT lanes. The idea is that under conditions of growing congestion breakdown of flow can be postponed if motorists are gotten to slow a bit with a lower speed posted on a variable message sign overhead. This has been in use for over a decade on portions of the M25 beltway around London Britain. There have been different evaluations of its effectiveness.

I-394 HOT lanes generally successful

The I-394 MnPass HOT lanes in operation since May 2005 have been extensively evaluated. They are a big success in terms of traffic management over the HOV lanes which they succeeded. And they now have a substaantial constituency of motorists who benefit from them on a daily basis.

Data before and after for six hours of weekday peakhour traffic (3 hours inbound in the morning plus three hours outbound in the evening) show that larger volumes of traffic are being carried faster, more reliably, and more safely with variable toll rates used to manage the volumes of single occupant vehicles.

Overall volumes in the managed lanes (managed as HOV before and as tolled HOT lanes now) are up 17% and volumes in the unrestricted lanes are up 3%, for a total increase in the corridor in these six peak hours of 5%. That increased traffic handled in the two three hour time slabs probably comes from either side of the three-hour peak and apparently represents traffic traveling when motorists most want to travel.

Free flow in managed lanes and 6% improvement in speed in free lanes

Under HOT the managed lanes are generally free flow and average speeds are up slightly by 0.9mph (65.6mph vs 64.7mph). The established transit and carpool users have no complaints about the tolled single occupant vehicles clogging the lanes, since the system effectively meters their numbers.

The unrestricted and free lanes while maintaining similar traffic volumes overall through the peak hours have benefited greatly by the overloads disappearing into the tolled lanes during peaks in the peakhours. Average speeds in the unrestricted/free lanes have gone from 58.9mph to 62.2mph - an increase of 3.3mph or nearly 6%.


Accidents appear to be down, though the evaluators say the sample of one year may be too short to be sure. Incidents dropped from 410 before to 355 after, about 14%. Clearly defined crossover zones between the managed lanes and the unrestricted lanes probably helped. (Previously crossovers were allowed anywhere.)

Also the reduction in the speed differential between the traffic in managed and unrestricted lanes may have helped reduce accidents. Merges are easier with smaller speed differentials.

Violation rates in the managed lanes are down sharply with HOT as compared to HOV before.

The lanes are divided into an eastern portion (east of TH100) with two barrier separated reversible lanes and a western portion of a single buffer separated concurrent lane each direction. Violation rates dropped from 7% to 4% in the reversible lanes and from 20% to 9% in the concurrent lanes. By contrast violations in I-35W HOV lanes are about 30%.

Enforcement benefits from double line buffers and the larger police presence that can be supported by the toll revenues.

The I-394 HOT lanes project managed to survive an early PR and political setback when the offpeak direction morning takeback of a lane in the mid section of the project caused new congestion, and a huge media and political uproar.

Engineers had planned an auxiliary lane at this location, but they hadn't focussed on how urgent it was if the lane was to be taken away. The political furore had the legislature force the project out of the planned 24 hour operations back to peakhours, peak direction operations.

The needed auxiliary lane got built by the end of 2005, and all flows smoothly now.

Toll rates in I-394 HOT lanes are set dynamically, based on monitoring the density of traffic (lane occupancy) and look-up tables which set toll rates at levels directly related to traffic density. The initial algorithm caused excessive fluctuations in toll rates and traffic. At times there was an unwanted cycling between too much traffic at low tolls and too little at high tolls.

A new algorithm smoothing the occupancy data and a new toll schedule has successfully damped the cycling. That was introduced at the end of 2005.

With six entry-exit points along its length this is the most complex HOT lanes facility in the US. There are a couple of direct connector ramps but mostly it depends on crossover zones with the free lanes where traffic weaves in and out. Most have worked well, though at one crossover a bus company complains that the merge is difficult for its buses.

The road is divided into two toll zones complicating the signing of changing toll rates as compared with 91 Express Lanes, I-15 San Diego and the Texas toll lanes which all have a single zone. But the two zone signing in MN/I-394 seems to work alright and be comprehensible to motorists.

The lanes opened May 2005 with 5,700 motorists in the corridor having accounts and installed transponders. The number rose to 9k by the end of 2005, and has edged up to just over 10k now.

The average use is two toll trips per week. Toll rates vary continuous between 25c and $8.00 by 25c intervals depending on what system algorithm estimates is needed to maintain free flow plus reasonable usage of the HOT lanes facility.

The average toll is about $1.10.

Revenue shortfall

Major disappointment is that revenue is much lower than expected. When the project was modeled it was estimated revenue would start in the range $2m to $2.5m maturing at $3m to $3.5m. Annual revenue in fact is running at just under half forecast - at just a bit over $1m.

Both traffic and tolls are lower than expected.

This could be partly due to the runup in gasoline prices and a slight uptick in bus travel in the corridor. Carpooling however is down.

In part the project seems to be a victim of its own success in managing traffic. By acting as a safety valve for traffic in the peak of the peak the managed lanes have so improved traffic flows in the free lanes there isn't the incentive they expected to use the toll lanes. Over the whole six hours of peak travel speeds in the managed lanes are only 3.4mph better than in the free lanes (65.6mph vs 62.2mph).

Compared to the one minute advantage over the 11 miles (18km) when it was an HOV facility there is barely a half minute advantage now.

WANTED: some real congestion, California style

Most of the time in peak hours motorists on I-394 MnPass are probably paying for greater certainty about their trip time than for any actual experienced time savings. Average trip times are 10.6mins in the free lanes versus 10.1mins in the toll/HOV lanes. Just a half minute difference!

With measured average speeds of over 60mph over six peak hours (6am to 9am outbound and 3pm to 6pm inbound) congestion is just not bad enough in the free lanes to generate major revenues in the toll lanes alongside.

BACKGROUND: Setting up the HOT lanes cost $10.7m. Operations cost some $1.8m in the first year. Enforcement is costing about $200k/yr. It had been hoped that revenues would cover operating costs but at present they are running $1m/yr short.

COMMENT: The HOT lane in the 3F/1T/1T/3F format (F=free, T=toll/HOV) does terrific work as a tool of traffic management. It does an amazing job over HOV of improving traffic operations.

However its largest benefits are accruing to drivers in the six free lanes and it is recouping no revenue from them. Maybe over the next several years if traffic grows the balance will change. But for now without tolling existing free capacity in say a 2F/2T/2T/2F format it looks unlikely to earn sufficient revenue to provide a return on investment.

Meanwhile, any lane takeaway to make this financially self-supporting is a tough political sell.

INFORMATION: For general information including the RFP for I-35W: http://www.mnpass.org/

The first formal evaluation of I-394 MnPass HOT lanes: http://www.mnpass.org/pdfs/394mnpass_tech_eval.pdf

To download a 9 page "Lessons learned" paper by Lee Munnich and Ken Buckeye.

TOLLROADSnews 2007-12-09

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