Roadshow: Solving freeway mysteries — what are those bars, slots, reflectors?

Q One time we were traveling on Interstate 80 in Nevada. There was construction, as usual. What was baffling us is what they were doing where they were installing some kind of traction aid in the right lane. There were two sets of three raised cement bars, one set for each side of the lane where you would typically drive. This was about every two feet.

It looked like it would be a great thing, for winter driving, until you drove on them. It was so rough that even truckers were avoiding the right lane. Could you shed light on this?

Susan Schubert

A According to the Nevada Department of Transportation, the blocks are a dowel bar retrofit. In new concrete paving construction, dowel bars (which look like rebar) are placed in adjoining slabs to transfer the wheel load and keep the edges from bending and cracking. That segment of I-80 was built before dowel bars were used, so the retrofit project cut the pavement, inserted the dowel bars and then covered it.

Q When traveling on Interstate 505 out of Vacaville to I-5, they were cutting uniform rectangle slots into the road about 6 to 8 per lane every 3 feet or so. They then buried a metal T-bar with a round cylinder into the slot and grouted over it. What were this things for? I thought maybe a test freeway for self-driven cars?

John Howard

Morgan Hill

A Nope. As in Nevada this was a construction project where they cut the slots and put in dowel bars to keep the slabs bound together, then they ground the concrete for a smooth transition.

Q I’m fascinated by weird roadway signs, markers, etc. I want to know what they’re about. I’ve seen some for a few years that I’m finally getting around to writing you about on new areas of I-205 and I-5 between Sacramento and Stockton.

About a quarter of a mile before most exits are a series of three reflectors on the shoulder aligned perpendicular to the road. Then about halfway from there to the exit are two reflectors perpendicular to the road. Then probably at the “legal start” of the exit is a single reflector. What gives? Obviously 99.9 percent of drivers would not notice these whatsoever.

Kevin Weber

Los Gatos

A The white reflective dots on the right are to alert drivers that an offramp is ahead, a helpful tool when thick fog makes it hard to see. Three side-by-side dots will appear three-tenths of a mile from an exit. At two-tenths of a mile, two dots will appear, and at one-tenth of a mile, one dot will appear.

You don’t see this in the Bay Area, where fog is less of a problem.

Q Driving up to Washington, I saw three reflector dots spaced a certain distance apart in the median of I-5. What was the significance of this?

Annie Brown

San Jose

A It’s another fog device, only for the Highway Patrol and other emergency crews. This tells the CHP and others that there is a median crossing ahead that is paved or lined with hard rocks, so they can make an emergency U-turn. It is helpful in fog, snow or at night and is usually used on flat stretches. The dots are 528 feet apart.

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