Show off.

February 5, 2007 11:07 PM

A motorcycle cop turned on the flashing lights and started weaving back and forth between cars on the highway. The passes kept getting wider, gradually prompting everyone to clear out of all 4 lanes and hang back about 1/4 mile behind him. Then he continued these sweeping 'S' maneuvers across the lanes for miles. By the time I had to exit, prevailing speed had dropped from 75 to 40. What was he doing, and why?
posted by nakedcodemonkey to travel & transportation (24 answers total)

Purely speculation, but he was probably slowing down traffic for something happening up ahead. Perhaps a special transport that had just got on a few miles up? Seems like an odd way to go about it though.
posted by saraswati at 11:14 PM on February 5, 2007

This happened to me outside Philadelphia (maybe Jersey?). They do this, I guess, to slow traffic down.
posted by catfishjohn at 11:22 PM on February 5, 2007

Traffic Break
posted by ApathyGirl at 11:22 PM on February 5, 2007

Oooh, high speed pursuit up ahead!

(In LA, at least.)
posted by thehmsbeagle at 11:31 PM on February 5, 2007

I think in the UK they call this a rolling roadblock. The intention is to slow the traffic down, or possibly stop it, because of something happening ahead.
posted by prentiz at 11:45 PM on February 5, 2007

It's also called a "rolling traffic break" or "rolling traffic stop".

More often than not (even in LA) it is something simple like debris or a stalled/stopped car, in which case they can often create the brief time they need to clear the lanes without actually closing any lanes or the freeway itself just by slowing the flow down for a bit.

Full closures (rare even in LA) and detours sometimes start with a rolling break and either a (hopefully) co-ordinated, planned lane by lane closure terminating in an exit and (hopefully) a planned detour/bypass around the closed freeway segment. This is usually used for emergencies like fuel truck crashes, accident fatalities or perhaps shootings that require forensics and analysis across all or most of the lanes.
posted by loquacious at 1:15 AM on February 6, 2007

I think everyone's covered it. I can only add that the one time this has happened to me, there was a very small construction cleanup crew that was driving along and picking up left-over materials and whatnot.
posted by spiderskull at 1:20 AM on February 6, 2007

Could be an escaped tiger.
posted by veedubya at 1:58 AM on February 6, 2007 [4 favorites]

They do it in France - Paris - also, on freeways entering the city (early in the morning). Slow all the traffic until it builds up and self moderates, then speed off leaving 2 kilometres of backed up, slow moving traffic - which remains so throughout the rest of the day. The French would drive at 180km/h right into the centre of Paris, otherwise ... ?
posted by strawberryviagra at 3:48 AM on February 6, 2007

This happened to me once in NJ, when up ahead there was a mattress (or two) and some other debris on the freeway.
posted by katie at 4:07 AM on February 6, 2007

Happened to me in LA ... suddenly five police cars enter the freeway in front of the rolling break , and another half dozen appear chasing a car off another freeway. They had traffic slowed down to about 20 miles an hour when they deployed the spike strips, and we got to see physics in acction as the car they were chasing tried to dent a concrete wall.

And then the five or six cop cars that didn't need to be there pulled over everyone with expired tags.
posted by SpecialK at 5:17 AM on February 6, 2007 [2 favorites]

Happened to me in NJ too. Scary isn't it? I thought the cop was going nuts and we were all in danger. Anyway, yeah, rolling traffic stop. Thats how they get the time to cone off lanes or whathaveyou.

Can you imagine setting up cones one by one at breaks in traffic?
posted by Brainy at 5:50 AM on February 6, 2007

Happened to me and found out it was a funeral procession.
posted by spicynuts at 7:03 AM on February 6, 2007

In Washington, D.C., the cops do this behind POTUS/VP motorcades on the Interstate highways.
posted by J-Train at 7:45 AM on February 6, 2007

Wow, interesting. Thanks everyone. (Brainy, yeah definitely unnerving at first.)
posted by nakedcodemonkey at 7:48 AM on February 6, 2007

This happened to me about six months after I moved to LA. It was about 2 in the morning and I was convinced that a drunk had stolen a police car and was driving like a maniac. I actually called 911 from my cell phone to report it. I'd never seen anything like it in Florida.

It turned out to be -- no kidding -- a dead cow in the road. How in the world a cow even got onto the 405 is still a complete mystery to me.
posted by GatorDavid at 7:53 AM on February 6, 2007

I was listening to a radio program about freeway traffic problems, when a caller said that increasing the speed limit would reduce congestion because every one would be off the freeway faster, and the guest traffic engineer replied that studies have shown that, because people increase their following distance so much in response to speed, 37 mph is the optimal speed for getting the most people to their destinations in the least time.
posted by jamjam at 8:53 AM on February 6, 2007 [1 favorite]

In LA I witnessed several of these on the 405 going to the airport. In one case it was for a motorcade sporting the South Korean flag, another time it was the POTUS (verified by news reports).

I wonder how big a big-shot you have to be before you get the honor of having traffic stopped for you.
posted by MonkeySaltedNuts at 9:26 AM on February 6, 2007

Happened to me and found out it was a funeral procession.
posted by spicynuts

Ditto, and when I've seen this, it was a for a police officer. Hundreds of cops cars and motorcycles driving single file at 25 MPH down a completely deserted freeway is an eerie sight.
posted by peep at 10:56 AM on February 6, 2007

"It turned out to be -- no kidding -- a dead cow in the road. How in the world a cow even got onto the 405 is still a complete mystery to me."


Probably wasn't dead when it got on the 405...
posted by stenseng at 11:56 AM on February 6, 2007

It's how cops (on motorcycles or in cars) stop traffic on a highway where cars are traveling at 65mph+. It works quite nicely.

It's standard procedure for the CHP here in LA, and usually used for very mundane things like an aluminum ladder in the HOV, or a stalled Toyota Cressida in the number 3 lane.
posted by turducken at 12:07 PM on February 6, 2007

Growing up in San Francisco, I remember PSAs (channel 2?) mentioning this, and I swear they called it "round robin". I didn't have much luck with the google (except this) but I distinctly remember it being called that.

The short story is that they would do that when there's an extreme hazard up the road (such as a cow, apparently). I don't recall it being used for traffic control.
posted by geckoinpdx at 12:39 PM on February 6, 2007

I saw this done once on 695 going towards 95 from Catonsville. They were doing it in order to completely stop traffic so they could put up some I-beams that completely spanned the highway. Freaky as hell.
posted by sperose at 4:11 PM on February 6, 2007

Possibly they were trying to break a standing wave in the traffic?
posted by tomble at 6:44 PM on February 6, 2007