Beltway speed signage explained
Rick Sambuco, who spent years before his retirement commuting between Villa Nova in the Liberty Road corridor and Bethesda, had a question about signage on the Beltway.
Traveling north on the inner loop of the Baltimore Beltway just past Exit 17 (Security Blvd.), there is a "SPEED LIMIT 55" sign on a tall wooden post. Just a few yards beyond the sign hangs the overhead electronic sign. Sometimes, there is an Amber Alert or a reminder to report suspicious behavior to a tip line. But most of the time it reads "I-83 10 miles, 10 minutes." Mentally doing the math, that's 60mph. A few yards beyond the electronic sign is a sign warning that a work zone lies ahead and that sped cameras enforce the 50mph speed limit. I find it funny that these three signs are presented one after the other in such close proximity. If I were a cynic, I would say it is done this way on purpose to increase the chance of getting a speeder on camera. But I really don't think it was done on purpose. Still, I find it odd.
For this I sought an received answers from two State Highway Administration spokesmen, Charlie Gischlar and Dave Buck, whose answers will be mashed up below.
There are speed limit signs placed at strategic locations throughout the Beltway, particular near interchanges where the speed limits differ (I-70 at I-695 is an example of this). Motorists driving eastbound along I-70 toward Baltimore travel at 65 MPH, which is the posted speed limit along I-70. The Beltway's speed limit drops to 55 MPH, so SHA has speed limit signs in close proximity to the interchange to alert motorists of the reduction in the speed limit.
First, the speed limit for I-695 (Baltimore Beltway) is 55 MPH. Speed limits are established using the 85th percentile, which is the speed at which 85 percent of the traffic is travelling. The real-time traffic time electronic displays are based on real-time traffic data/conditions. Although 85 percent of traffic is travelling near or at the prescribed speed limit, 15 percent of motorists are traveling at a rate greater than 60 MPH. The display will never show a time below a prescribed rate of 60 MPH.
SHA reduces speed limits in work zones across the State for the safety of our crews and motorists and their occupants.
SHA's number-one priority is safety for all highway users. Highway work zones are dangerous places for SHA and contractor crews, as well as for motorists who travel through them. In highway work zones, motorists may encounter lane shifts, slow moving construction equipment or narrowed lanes. In four out of five cases of a work zone crash, it is the motorist or occupant who are injured or killed by not taking precautions driving in a work zone. There is also the family of an SHA or contractor work crew that will be minus someone at the dinner table because of aggressive driving through work zones. SHA's Safe Zones Program of automated speed enforcement is a tool used to change driver behavior to slow down approaching and travelling through a highway work zone. There are warning signs placed in advance of the work zone, as well as speed trailers that display travel speeds with the prescribed speed limit below, which enables drivers to know in advance how fast they are traveling. There is no excuse for speeding through a work zone.
Each sign at this location has its own purpose.
The speed limit signage is permanent and at placed pre-determined intervals on I-695 (actually, on all roads). SHA particularly makes sure there are permanent speed limit signs just after major interstate to interstate junctures (i.e. 695 just past I-95, just past I-70, just past I-795, just past I-83 etc...)
The work zone signage is temporary and just as the portable speed camera vehicles will be taken away once the project at Liberty Road in completed, so will the temporary signage.
As you know, our overhead message signs have displayed a wide range of messages over the years and we continue to hear positive feedback about the estimated travel time messages.
However, a message on the overhead message board saying it takes approximately (not exactly) 10 minutes to go 10 miles in no way infers "Hey, let's speed up because traffic is cruising along..." It's a snapshot of the current conditions over quite a long stretch of road, where conditions can and do change rapidly. And, it's an approximation based on conditions at that very second.
It's safe to say anyone traveling along I-695 between Security Blvd and I-795 will not get a speed camera violation at 60 mph since the threshold is 62+ and they will arrive 10 miles ahead in about 10 minutes, as long as conditions remain constant.