Who’s causing congestion on I-66? Hybrids or scofflaws?
Photo by afagen on Flickr.
An informal count of cars on I-66 in Arlington just east of Sycamore Street seems to indicate that the clean-fuel exemption may be a factor in slowing traffic down without providing significant transportation value.
Hybrids and other clean-fuel cars are exempted from the HOV requirement on I-66. All vehicles inside the Beltway on I-66 must be HOV-2, be a motorcycle or have a clean fuel exemption license plate.
Dr. Gridlock has suggested removing this exemption to help the HOV lanes function better. I believed instead that the problem was caused more by scofflaws—single occupancy drivers illegally on the road—than the hybrid cars, based on times I drove on I-66 and observed the cars around me.
Recently I had a chance to test this presumption. I was crossing over I-66 on the pedestrian overpass near Madison Manor Park (map).
I tried to count how many cars were scofflaws but soon realized that it was difficult to tell if there was a child in the back seat or not. Also, many of the cars had the clean-fuel license plates
From this vantage point, the license plates could be read fairly easily, so I chose to count the plates instead. Traffic seemed to be traveling about 30-40 miles per hour, slower than free-flowing.
Plates with CF, CX, CY or CZ are exempt from the HOV requirement. (One can have a vanity plate exempted, too, but there were few of these; but how should one count the car with the plate GOVEGAN?) The following cars passed between 8:04 and 8:10 AM:
- 333 cars: 67 with clean-car license plates; 266 without.
- 1 motorcycle
- 2 buses
- 1 18-wheeler! (which are illegal on this highway)
- 1 eastbound 6-car Metro train
Of the cars, 67 had clean-fuel license plates, approximately 20%.
Here’s some quick math extrapolating to an hour and making some assumptions:
- 2700 HOV cars with 2.2 riders = 6,000 people
- 670 clean-fuel cars with 1.1 riders = 750 people
- 20 buses with 40 people = 2,000 people
- 10 Metro trains with 800 riders = 8,000 people
The clean-fuel cars represent less than 5% of the people being transported along this corridor but represent 20% of the cars. Would removing that 20% increase flow enough or more than enough to make up the difference? Would increased flow entice more HOV cars onto I-66?