Thursday, April 5, 2018

Weekend testing of Mercer Street ramp meters to I-5 prove beneficial to freeway traffic

Flow can still benefit with help of drivers

By Harmony Weinberg

With four weekends of ramp metering from Mercer Street to Interstate 5 in the books, we have seen the system prove itself as an effective tool to help manage freeway traffic. Our goal is to keep the area moving as safely and efficiently as possible. Initial testing also shows drivers are still adjusting to the changes and are not fully utilizing all lanes approaching the ramp meters. In order to give drivers more time to get comfortable with the new meters and for us to install additional signage, we are pushing back our original launch date of weekday ramp metering by a week to Tuesday, April 17.

The Mercer Street ramp meters lit up for the first time on Saturday, March 10. We spent the past four weekends monitoring the new meters and refining the operation to best fit travel patterns.

New signs on the way
To help make the addition of ramp meters to the area more visible to drivers, we will add new temporary signs to both the north and southbound ramps to I-5 before we turn the meters on during the week. We observed on Saturdays and Sundays that drivers heading northbound onto I-5 were hesitant to use the left lane. When the meters are on, a sign flashes to advise folks to use both lanes. We expect that additional signs will grab drivers’ attention even more. Within the next few weeks we will also be installing an electronic sign on the northbound ramp to further alert drivers that they can use either lane approaching the ramp meter.
Drivers hesitate to use the left lane when the northbound ramp meters are activated.

When the meters activate on the southbound on-ramp, drivers can spread out into three lanes thanks to the use of the shoulder. While we saw some folks use the left shoulder, we expect drivers to take full advantage of this option as they continue to get used to the new meters.
Drivers are encouraged to use the left shoulder lane when the southbound ramp meters are activated southbound.
When and why did the ramp meters turn on?
Remember, the ramp meters don’t just turn on at a specific time each day. Instead, they turn on when the system detects traffic slowing down on I-5. When it comes to a typical weekend, we likely won’t see the ramp meters turning on as much as they will when more vehicles are on the road during the week.  This has proven out so far on weekends, where the meters have automatically activated at different times of day depending on how I-5 was operating and how much Mercer Street traffic was entering I-5.

Effectiveness of ramp meters following crashes
Ramp meters really show their effectiveness when it comes to managing traffic following a crash. We saw three crashes over the first weekend where the ramp meters did their job. They allowed for one vehicle at a time to merge onto the interstate where traffic was backing up due to a crash ahead.

What about Mercer Street traffic?
We know many of you had concerns that the ramp meters would make traffic worse on Mercer Street. We worked closely with our friends at the Seattle DOT to monitor city street traffic and saw no impacts from the new meters. It’s important to understand that the meters are allowing the same number of vehicles onto the freeway as before; they just break up the pile of cars trying to merge and organize them in a manner that has less impact to the flow of traffic on I-5.

Recap: why we meter
The largest benefit of the Mercer Street ramp meters will be at the beginning and end of the peak commute times. The meters prevent big groups of cars from piling onto the freeway at once, which will keep I-5 flowing smoother during those times.

When congestion reaches the peak, severely slowing freeway traffic, ramp meters are not as effective. However, we keep the ramp meters on in order for them to quickly adapt to changing traffic conditions and help the freeway recover quicker by pacing the merging vehicles onto the freeway.


Meloyanik said...

Thanks for this. I've only been there once since the meter started, and didn't know about the extra lanes. I'm glad I am reading about it now so I look smart next time : )

RunnningFreee said...

What's the motorcycle policy in the metering system on Mercer? Would increasing moped, scooter, and motorcycle commuters also be an effective way to reduce traffic? Is there any data on this?

Unknown said...

Unfortunately but predictably this had been a huge failure. It's done nothing to ease the number of cars entering I5 southbound but had created mass confusion when three lanes now try to merge into one on the ramp as well as on Mercer where no one allows you into the backed up right lane anymore and you're faced with cutting someone off in the Mercer Fairview intersection or being fixed onto NB I5! What a headache

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