HomeCommunity NewsEngineer Explains Huntington Drive Signal Patterns

Engineer Explains Huntington Drive Signal Patterns

Traffic flow along Huntington Drive has increasingly become a focus of conversation as population growth has increased in surrounding cities and more cars have flowed along and across it. Concern over traffic circulation has also increased recently as the Los Angeles County Metropolitan Transportation Authority (Metro) has offered San Marino $32 million from Measure R transportation funds. The monies are meant to address traffic impact stemming from Metro’s decision to not construct the 710 freeway tunnel project. The tunnel project aimed to link the 710 and 210 freeways. Metro has suggested a traffic light synchronization program, but residents are wary.

Parks and Public Works Director and City Engineer Michael Throne shared with The Tribune insight on the current operation of signal timing and how it was established.

Throne noted that the county does not direct the city with signal control. They are city owned, save for the San Gabriel Boulevard intersection and the South Pasadena/Alhambra bordering intersections, where San Marino works with the neighboring cities who share ownership of the intersections. The current timing setup of delay, or red lights, was set approximately five years ago in the city. The times were set after a traffic study was completed and an engineering analysis of each intersection was considered, taking in volumes and times of day into account. Throne explained that there are generally accepted practices in the traffic engineering field as to how much delay is set to different legs of intersections.

“The maximum amount of time you could be delayed at a traffic signal is 2 minutes and 30 seconds,” Throne told The Tribune. “That is the accepted norm for traffic signals. It may seem like it’s longer, but it’s not.”

He noted that any time longer than that speaks to faulty equipment. The maximum time is a national standard and is established by the Institute for Transportation Engineers. According to Throne, traffic signals grew in popularity in the 1950s and are generally based on traffic behaviors on primary roads.

The signals operate based on two types of sensors to provide information if someone is waiting at a light. The first are electromagnetic sensors, which are loops of wire buried in the pavement that sense when a car is pressing upon them.

“It’ll sense that you’ve entered into field and it’ll say ‘oh something has to happen with that vehicle,’” said Throne.

The second are optical sensors, such as one located at Huntington Drive and Sierra Madre Boulevard/San Marino Avenue.

“There’s a camera pointed at the approaching lanes and the camera through special programming, the computer goes, ‘oh there’s four cars there it’s time for me to start changing the signal,’” explained Throne. “It’s much more reliable than loops in pavement.”

The engineering study for establishing the pattern takes into account how many cars go east-west and north-south, pedestrian crossing needs and turn lane times.

“You put this into a process where you try to balance out all of the needs of all of the users of the intersection so none wait longer than that 2 minutes and 30 seconds,” Throne shared. “Priority is given to the main road always because that’s the road where you have the most cars.”

During offpeak hours, the signal operates “pretty much on demand” so a car approaching a signal, say at 2 a.m., will receive a green light fairly quickly. During peak times, the programming set five years ago makes the signals operate under the theory that the traffic flows the same way at the same times during the weekdays.

“Our signals are not connected together so therefore their programming was the estimation of several years ago of how they should operate during the commuter hours,” said Throne.

Throne noted that signal programming, when set individually, can be outdated within a year due to an increase of land use in neighboring areas, such as a business area development or residential construction. Setting an annual process where each signal is readjusted is expensive and not assured to capture every variable, according to Throne.

“When you have 15 signals, all on major roads, that becomes a much more laborious task and it really becomes not practicable anymore,” said Throne.

The process to alter traffic signals involves the city traffic engineer taking traffic counts over a 24-hour time period over the course of 2-3 weeks to capture what the normal flows are in different directions at various times, including pedestrian and bicycle counts. With that information, the traffic engineer manually designs a system that each signal would go off of for certain times of the day.

According to Throne, the degree of change for the signals could either be made directly by the traffic engineer for small adjustments or would require a city meeting process for more major ones.

“If it’s just a tinkering with a couple of seconds here or there, no one’s going to overtly sense that there’s a difference there, maybe a little bit, but any wholesale major change we could go through the Public Safety Commission and then the City Council,” said Throne.

Currently the city is undergoing a signal controller replacement program, as the ones in current operation are becoming more expensive to maintain month-by-month than to replace with current technology. Two have been replaced and Throne is hopeful that the City Council will approve two more in the next fiscal year.

The city is also looking at doing timing modifications at the St. Albans Road intersection with Huntington Drive, a community request, and is currently within a cost gathering stage to change the hardware.

Throne noted that the current signal controllers and equipment have a drawback in that they “don’t have a far look ahead” and only take in cars within a limited area.

“You can test this out,” said Throne. “When you’re on Huntington during the middle of the day and you want to make a left off of Huntington onto any of the side streets that are signal controlled, you can stop the cars that are racing towards you down Huntington. You can stop them if they’re just far enough away. For one car. That is not signal synchronization. The reason people speed up is they feel they have to hit the light.”

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