Q. Why can’t you find the sign, Route 108/Point Judith/Scarborough, on Route 1 North in South Kingstown like you can on the Route 1 South side? I have given many out-of-state motorists instructions from Snug Harbor and Jerusalem who are looking to take the ferry to Point Judith, Scarborough, or the Block Island Ferry. Giving them directions, I would tell them to go back to Route 1 and go north to the Route 108 Point Judith/Narragansett exit. A Route 108 sign needs to be added to the exit sign on the north side of the highway.

A. The signs that you are referring to on U.S. Route 1 in South Kingstown are called Exit Direction Signs. According to the Manual of Uniform Traffic Control Devices (MUTCD), an exit direction sign informs motorists of the route and destination information for the next exit, and also indicates whether they exit to the right or the left for that destination.

Prior to an Exit Direction Sign, drivers will typically see an Advance Guide Sign, which gives motorists notice well in advance of the next exit. These signs also inform motorists of the main destination served by that exit, as well as the distance to that exit. These signs are always followed by an actual exit sign at the point of departure from the highway.

The particular signs you mention are on Route 1 prior to the exit for Route 108, which leads toward destinations such as Point Judith and Scarborough. The Exit Direction Sign in the southbound direction indicates this destination information, and includes a State Route symbol for Route 108. In the northbound direction, however, the Exit Direction Sign only indicates the destinations reached by that exit, Point Judith and Scarborough, and does not include the State Route symbol for Route 108.

To the best of our knowledge, this issue was probably overlooked when the signs were installed in the mid to late 1970s. To rectify this RIDOT’s Maintenance Division will be notified to revise the sign on Route 1 North to include the State Route symbol for Route 108.

Just a matter of timing

Q. Please tell me that the new traffic lights installed on Route 1 between Charlestown and Westerly are going to be switched to trip lights. Right now they are cycle lights that disrupt the flow of traffic. One of the lights turns red every two minutes or so and the same seems to be true for all of the new lights. Please tell me this is going to change soon.

A. This question is a good opportunity to explain how traffic control signals work. Traffic signals that operate as pre-timed signals (which cause side streets to get a green light on every cycle) can be frustrating to motorists on U.S. Route 1 and elsewhere because drivers have to stop when there is no crossing traffic. Actuated signals operate differently and are more desirable.

With an actuated signal there are vehicle detectors on every approach to the intersection. The signal is usually programmed so that the green light will default to the main roadway, and the side street will only get a green light if a vehicle pulls up on the vehicle detector. Therefore, an actuated signal reduces delays on the main roadway, which in turn reduces gas consumption and fuel emissions.

The vehicle detectors are the key component of an actuated traffic control signal because they tell the signal when vehicles are present, and can adjust the green time according to the number of vehicles trying to cross through the intersection. New vehicle detectors were recently installed on Route 1 in Charlestown and all the new signals are now operating as actuated, rather than fixed time. (My guess is that you wrote this note before the construction was completed.)

Vehicle detectors can not be installed until the final pavement surface is laid down. Once the final surface is in place, the Department cuts the pavement and places the vehicle detectors in their appropriate locations. Because the pavement must also be a certain temperature to install the vehicle detectors properly, when there is a large installation of a traffic control signals, there is usually a period of time where signals need to operate on a fixed cycle time.

Dana Alexander Nolfe, chief public affairs officer for the state Department of Transportation, has agreed to answer questions of general interest posed by Journal readers about state roads and other state transportation matters.

The DOT is responsible for the state’s transportation infrastructure, which includes highways, bridges, traffic signals and bikeways.

To ask a question that would also be of interest to other readers, send a letter to Ask RIDOT, Features Department, The Providence Journal, 75 Fountain St., Providence, RI 02902. You can also e-mail your question to projocars@projo.com. Please put “Question for the DOT” in the subject field.

Questions or complaints of a specific nature should be posed to the DOT directly and will not be answered in this column.