Photo by Eric Keith / St. Joseph News-Press / Purchase this photo

Downtown motorists know the frustration of sitting at a stoplight when there are no other vehicles around.

The light is always greener in the other lane.

All motorists have experienced their share of frustration on the road. Like the driver who won’t signal for a turn, the guy who tailgates with his high-beams on, or the person who slows to 10 mph at the first hint of rain.

But for many drivers, the most annoying part of a trip is a red light. Either they last too long or turn at the wrong time.

Gayle Sellers said lights forced her to wait nearly five minutes to pull out of Burger King as she tried to reach East Hills Shopping Center on Wednesday. She said the lunch hour traffic backed up from the intersection of Frederick Boulevard and Belt Highway, preventing her from pulling onto the street.

“It seems like they could fix a lot of problems if they just made the green light longer,” Ms. Sellers said.

As any traffic engineer will point out, it’s not that simple. A longer green light for one driver means a longer red for another, causing lines of cars at the light.

The Institute of Transportation Engineers estimates the United States has about 300,000 traffic signals and predicts 75 percent would benefit from updated equipment or adjusted timing mechanisms.

Efficient signals guide motorists to their destination with few stops, save time and fuel, and reduce greenhouse gas emissions.

Traffic engineers measure traffic patterns to determine how signal cycles should operate at each intersection.

Bruce Woody, director of public works for St. Joseph, explained the traffic tools the city uses. The city’s traffic signals come in two basic types: fixed and actuated.

Fixed signals operate on a timer that alternates the right of way between lanes at set intervals, regardless of the number of cars waiting in line.

“Those are really only used when there is a fairly isolated intersection, when there isn’t enough traffic to justify changing times,” Mr. Woody said.

Timed signals can have multiple settings for different times of day. For example, some revert to a flash setting at night that allows traffic on the main street to proceed through a flashing yellow, while cross street traffic has a flashing red that functions like a stop sign.

Actuated signals, unlike their fixed counterparts, have sensors that help the traffic signals adjust to the flow of traffic. Older signals have a loop detector buried under the street that detects when a vehicle is waiting at an intersection. Newer signals use a low-resolution lens — visible above the traffic lights at many local intersections — that detects variances in light intensity that indicate the presence of a vehicle.

“A lot of people call them cameras by mistake,” Mr. Woody said. “It doesn’t record anything, it doesn’t take pictures for red light violations, it doesn’t do anything enforcement-related.”

The sensors can streamline traffic flow in several ways. If no vehicles are detected in a left turn lane, the green light for that phase of the signal cycle will be shorter or eliminated altogether. If a long line is detected, the sensor can add time to the green light.

On busy roads, signals can be coordinated to move groups of cars through multiple intersections in a row. This works well when one municipality maintains all the stoplights on a stretch of road. However, many of St. Joseph’s busiest roads require cooperation between the city and the Missouri Department of Transportation.

MoDOT maintains all signals along Belt Highway, Riverside Road, Frederick Boulevard and other streets that double as state highways. State signals adjacent to city ones must be able to communicate so traffic can flow smoothly.

“If two signals are too close to where the stacking of vehicles can overlap, we try to put in some sort of interconnection between the two,” Mr. Woody said. “We have to coordinate where we can.”

Clinton Thomas can be reached at clintonthomas@npgco.com.