Mass Pike's LeBovidge: we may have an overcharging problem, but we may not, we're working it

Alan LeBovidge CEO of the Massachusetts Turnpike Authority told us this week he has not been saying much about the swirling controversy over overcharges "because I'm not sure we have a real problem." He concedes there may be a problem, just that until the data has been thoroughly analyzed it doesn't make sense to comment.

He says that there is a lot of information being bandied about as mistakes in the toll system that turn out to not be mistakes at all. And lots of confusion.

He's right. The AP quotes an official as saying that "during bad weather the camera meant to read the number of axles on a vehicle can be covered with grime or snow and misread its target."

Cameras don't count axles

But cameras don't read the number of axles, they read license plates.

A glance at their orientation shows they are aimed down the road to image the backs of vehicles (and in some places up the road to image the front of vehicles.)

Cameras are not pointed across the road to image the side of vehicles where the wheel and axle numbers could be counted by imaging, and image recognition. (There have been efforts to do this with lasers but they have not been very successful.)

Treadles and light curtains classify vehicles

Axle count is done on the Massachusetts Turnpike and many other traditional tollroads by treadles in the pavement registering each axle pass and by light curtains designed to sense the beginning and end of each passing vehicle including a trailer hitch if it has a trailer. 

The treadles sense and count wheel hits. Their data must be coordinated with the vehicle sensing curtain of light and receptors on the opposite side of the lane. These sense when the "curtain" of light is broken and when it is restored by the vehicle presence.

They are called generically 'presence detectors' and 'vehicle separators.'

By detecting the beginning and end of the passing vehicle they can associate a certain axle count with a discrete vehicle.

When they are working right!

The light curtain windows or glass faces are liable to get covered with grime over time. Quite quickly in wet conditions. And when there's snow the roads are usually salted, and salt drifts onto the light curtain windows.

They need regular cleaning.

And treadles wear. They are pounded by vehicles wheels, often in braking mode, so their exposed contact strips wear down. Their housings are set in the pavement so they get flooded by rainwater and get silt and salt washed into them.

Treadles need regular maintenance and replacement of worn parts.

The AP reported the equipment faults cause overcharging, cars being charged as trucks. True. If a light curtain fails to establish the separation between two vehicles then one gets charged as if had four axles - a tractor-trailer rate. What AP doesn't say is that there is also an undercharge - one of the two vehicles goes toll-free because of the failure of vehicle separation.

AP style reporting encourages paranoia

The paranoid notion AP encourages is of the greedy Turnpike making money while motorists are shafted. In fact motorists are randomly overcharged and given free rides.  The Turnpike makes no money out of faulty equipment.

Similarly if a treadle goes bad it is just as likely to fail to register an axle pass and to undercharge the motorist as to register too many axles and overcharge.

Connaughton rule - default to lower class

Mary Connaughton, a director on the board of the Authority has suggested that in cases where there's a difference between the the vehicle class in the transponder account and the vehicle class as read by the lane equipment - that treadle/light curtain combination - the toll charged should be the lower of the two classes. The Turnpike's customers should get the benefit of the doubt.

That seems fair.

Only problem with the proposed Connaughton rule is that it could encourage a common kind of cheat - the trucker who registers a car account and then sticks the transponder registered for a car on the windshield of his 18-wheeler.

Our opinion: there's no good substitute for well-maintained equipment.

REVISION: Since this was published we've had several calls and emails pointing out that our account is not completely accurate and is oversimplified so we'll be revising it. Monday 10:00

TOLLROADSnews 2009-03-06