How is highway traffic entirely stopped?

September 1, 2009 5:26 PM

How do the police/traffic authorities stop a moving highway/motorway?

Often you see highways/motorways that have had cones placed across some or all of them. My question is how do the authorities accomplish this - they can't simply place cones down because of the fast moving traffic behind, nor can they really wait for a quiet bit since without warning signs it would create a hazard. How is a fast moving motorway 'stopped'?

posted by cdenman to Travel & Transportation (13 answers total)

Best answer: I've seen this happen in Los Angeles. A cruiser with full light and siren begins changing lanes in a zig-zag pattern until it has slowed traffic down to a stop. As traffic slowed, the cruiser began to actually weave across the highway. It was surprisingly effective.
posted by mrmojoflying at 5:28 PM on September 1, 2009 [1 favorite]

Rolling Road Block
posted by benzo8 at 5:30 PM on September 1, 2009

Best answer: What mrmjojflying said. I was on the New Jerey Turnpike once and got caught in a similar stop. Two police cars pulled out, each straddling the middle of two lanes (it was a four lane highway there). They wove back and forth and slowed down to a stop. The we sat there for an hour, and then they left. I don't know why.
posted by procrastination at 5:33 PM on September 1, 2009

Yeah, I've seen this happen a couple of times - it's impressive, really, how quickly people catch on and slow down. In the two instances I've been a driver when this has happened, it was done in order to clear accident debris from traffic lanes, and delays were minimal.
posted by rtha at 5:38 PM on September 1, 2009

Referred to in California (maybe elsewhere) as a traffic break, and conducted per mrmojoflying's description.
posted by rkent at 5:57 PM on September 1, 2009

Another Angeleno here. An officer reverse parked his cruiser on a hill with his lights flashing. We were shunted from six lanes to two, with a line of cones and about six officers waving at us not to look as we slowed. Gasp. A BMW had hit a produce truck and there was produce everywhere. No human injuries. A crew sweeping vegetables off the freeway. Suddenly, I am driving through cucumbers, watermelons, tomatoes. I could barely contain myself. Better than Fellini.
posted by effluvia at 5:58 PM on September 1, 2009 [3 favorites]

Best answer: I've seen this happen in Los Angeles. A cruiser with full light and siren begins changing lanes in a zig-zag pattern until it has slowed traffic down to a stop. As traffic slowed, the cruiser began to actually weave across the highway. It was surprisingly effective.

I've seen it happen in LA and it's pretty awesome, but the asker did use the word "motorway" so I'm guessing some international angle might be at play. For what it's worth this technique is not used in the United Kingdom at all. Instead, the cops will merely get ahead of traffic and slow down. (Undertaking is illegal in the UK and people just tend to stop when cops are around anyway.)

That said, I've actually seen them putting the cones out at night without using cops on otherwise open motorways. They have a truck with yellow flashing lights on the back and "move right" signs, slow down, and a guy starts dropping cones off the side (there has to be an art to this). The truck then moves along slowly as cones are dropped, and they move across the lanes as necessary to achieve this. Typically the digital motorway signage is used to get traffic to move across the lanes and slow down to ~50mph a mile or two before this so that drivers are aware they need to move across.

If you drive on the British motorways late at night it's not uncommon to be going through roadworks that suddenly end and you see a truck with a dude dropping the cones off as you're literally steaming through.. :)
posted by wackybrit at 6:36 PM on September 1, 2009

For what it's worth this technique is not used in the United Kingdom at all. Instead, the cops will merely get ahead of traffic and slow down.

Note, I'm not saying they don't do rolling roadblocks, as they do. They just don't do the whole crazy weaving stuff :)
posted by wackybrit at 6:38 PM on September 1, 2009

Just chiming in that I've seen both all of I280 and I101 shut down with the zig-zag method. It takes a few miles, and exploits people's natural tendency to slow down when emergency lights are flashing. As they change lanes, the people up front pick up on what's happening pretty quick and the whole thing grinds to a halt. By the end, the cop car is moving practically back and forth (like a high frequency sine wave) as opposed to changing lanes.

This is just for shutting down the whole thing, though. Shutting down one lane generally happens organically (that is, someone broke down obstructing it), or can be done by putting up signs and cones, usually at night. I've seen the trucks laying them out, but not how they start this. If I had to guess they would set up some warning signs first, and then have a highway patrol with emergency lights on obstruct the lane while someone ahead creates the cone merging lane. It does seem risky, so I'm curious if there's more to the method.
posted by cj_ at 6:58 PM on September 1, 2009

Highways Agency Traffic Officer in the UK here. I work on the motorways in liveried 4X4s and do this on a regular basis.

Interrupting the flow of traffic on the motorway can be due to some kind of planned event. These will be scheduled when traffic is light (though therefore fast) - generally at night. These closures must adhere to chapter 8 of the Traffic Signs Manual in the UK which defines exactly what forewarning of lane closures is needed and the distances involved. These advance signs are obviously set up first, then a vehicle with direction arrow and crash cushion on the back (known as a Traffic Management or TM vehicle) will be positioned and start to drop the cones to physically close the lanes as defined by Chapter 8. These vehicles are not allowed to work in the running lanes without the advance warning signs or a rolling road block to create a sterile area for them to work in.

Alternatively, the flow of traffic may need to be be interrupted due to an unplanned danger: debris in carriageway; stranded vehicle in running lane; Road Traffic Collision; Air ambulance landing; immediate barrier repairs needed; pot holes need filling etc. This is what the Highways Agency Traffic Officers and the police manage and execute. If for any reason a person needs to access the carriageway a sterile area needs to be created and this will be done using a rolling road block as others have described.
posted by hmca at 5:52 AM on September 2, 2009

cj, I've seen the beginning of the process, and it's pretty much as you describe. It does seem risky. Another oddity is when one comes across a moveable-barrier truck in action.

I've been slightly in front of a rolling road block, and it's really creepy. I pulled onto the highway from an entrance ramp one morning and noted an odd absence of traffic, like, I was the only car on the road. This was on the DC beltway around 9:00 am on a weekday, so I did realize sometihng was up, but, you know, I was thinking about getting to work, so I didn't over-think it. I glanced in my rear-view mirror, and saw the roadblock behind me--a couple of cruisers with their lights on, blocking an immense number of cars, moving, but slowly. As I began to figure out what was going on, I came upon an accident scene with a car pointing in the wrong direction.
posted by MrMoonPie at 5:58 AM on September 2, 2009

For more about Highways Agency Traffic Officers
posted by hmca at 6:06 AM on September 2, 2009

Thanks, hmca. Out of curiosity, how often (if at all) do those TM's get run into when they begin to lay down the cones? It seems to me that late at night, you're going to have people (a) going much faster and (b) more tired/intoxicated, and therefore not notice the signs. Is the brightly-lit arrow sign on the back enough to get people out of the way?
posted by cj_ at 1:49 AM on September 4, 2009