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January 01, 2016

Speed Limits, Safety and Fuel Efficiency



Crawling along I-95 the other day in the usual bumper-to-bumper traffic, I snickered when I noticed the “Speed Limit 55” sign alongside the highway.  I wish!
Of course, when the highway is not jammed, speeds are more like 70 mph with the legal limit, unfortunately, rarely being enforced.  Which got me thinking:  who sets speed limits on our highways and by what criteria?
Why is the speed limit on I-95 in Fairfield County only 55 mph but 65 mph east of New Haven?  And why is the speed limit on I-84 just 55 mph from the NY border to Hartford, but 65 mph farther east in “the Quiet Corner”?  Why does the eastern half of the state get a break?
Blame the Office of the State Traffic Administration (OSTA) in the CDOT.  This body regulates everything from speed limits to traffic signals, working with local traffic authorities
(usually local Police Departments, mayors or Boards of Selectmen).
OSTA is also responsible for traffic rules for trucks (usually lower speed limits) including the ban on their use of the left hand lane on I-95 in most places.
It was the Federal government (Congress) that dropped the Interstate speed limit to 55 mph in 1973 during the oil crisis, only to raise it to 65 mph in 1987 and repeal the ban altogether in 1995 (followed by a 21% increase in fatal crashes),  leaving it each state to decide what’s best.
In Arizona and Texas that means 75 mph while in Utah some roads support 80 mph.  Trust me… having recently driven 1000+ miles in remote stretches of Utah, things happen very
fast when you’re doing 80 – 85 mph!
About half of Germany’s famed Autobahns have speed limits of 100 km/hr (62 mph), but outside of the cities the top speed is discretionary. A minimum of 130 km/hr (81 mph) is generally the rule, but top speed can often be 200 km/hr (120 mph).
Mind you, the Autobahn is a superbly maintained road system without the bone-rattling potholes and divots we enjoy on our highways.  And the German-built Mercedes and Audis on these roads are certainly engineered for such speed.
American cars are designed for maximum fuel efficiency in the 55 – 60 mph range.  Speed up to 65 mph and your engine runs 8% less efficient.  At 70 mph the loss is 17%.  That adds up to more money spent on gasoline and more environmental pollution, all to save a few minutes of driving time.
But an even bigger for the loss of fuel efficiency is aerodynamic drag, which can eat up to 40% of total fuel consumption.  Lugging bulky roof-top cargo boxes worsens fuel economy by 25% at interstate speeds.  So does carrying junk in your trunk (or passengers!):  a 1% penalty for every 100 pounds.
Even with cheaper gasoline, it all adds up!

1 comment:

H Stowe said...

As a former Connecticut resident, I can remember when Governor Meskill lowered the speed limit statewide to 50 mph in response to the energy crisis of 1974. I guarantee, that move did not affect my parent's driving speeds at all. In 1974, congress and Nixon made a 55 mph national speed limit a permanent annoyance for 21 years until it was repealed in 1995. As a result of the 55 mph speed limit, the number of speeding tickets issued doubled and then tripled in the ensuing years. Millions of drivers lost their licences for driving speeds that were legal in 1973. The reason for the lowered speed limit was ostensibly to save gas. How did it do? According to the Energy Information Administration statistics, fleet fuel mileage fluctuated from 11.9 to 12.4 mpg from 1970 to 1976. It did not break 13 mpg until 1979, as the vehicle fleet was replaced by cars tuned for fuel efficiency. The 55 mph speed limit was a massive failure in improving gas efficiency. Although driving speeds were reported to have dropped from an average of 65 mph in 1973 to 58 mph in 1974, fuel consumption barely budged. The 55 mph speed limit disrupted the smoother traffic flow that we had a year earlier and bred a new type of driver: the left lane bandit, which caused the majority of the acceleration and deceleration. Increased speed variance and a transfer of traffic to secondary roads also caused the fatality numbers to increase during the 1970's despite safer automobiles. The number of fatalities on the country's highways increased from 46,000 in 1974-75 to 51,000 by 1979 (almost the 1973 level of 54,000). In 1974, the fatality rate was 3.3 deaths per 100 mvmt. By 1979, it was 3.5. The death rate numbers wouldn't budge significantly lower until after the 1981 recession when police began directing their enforcement resources away from speed limit enforcement to drunk driving. By 1995, the death rate dropped to 1.70 deaths per 100 mvmt. Today, with over 40 states posting speed limits of 70 mph or higher, the death rates is in the low 1's. Fleet fuel efficiency is at around 25 mpg. Lower speed limits were responsible for none of it.