Q I just had to let you know that this smoke-belching truck with its exhaust pipes positioned vertically between the cab and the rear was in front of us and countless hundreds of other grimacing drivers driving on Highway 101 a couple of weeks ago. We all had to suffer through the horrible black smoke in traffic just north of the Golden Gate Bridge.

Then, what joy. A CHP finally pulled it over near San Rafael. You could almost feel the smiles on the faces of those in the cars around us. Some days, there is justice.

S.C.

Campbell

A A few days ago Dixie Sala, of Martinez, wrote in about an old pickup truck with its exhaust pipe modified so that it was sticking straight up out of the bed. "It was pouring -- and I do mean pouring -- thick black smoke out of it," Sala said. "People were also scrambling to get away because it was nasty smelling."

That prompted a flurry of responses.

Q I feel compelled to respond to Dixie Sala's letter and your response regarding black truck exhaust coming out of the modified exhaust pipes on a pickup. I have seen pickups with these modifications before; they are called stacks, and resemble exhaust pipes of semi trucks.

There is nothing "incredibly stupid" about these pipes; the driver has added this harmless modification to reflect his love of semis. These vertical pipes are there for a reason, much the same as the tall stacks on locomotives: to vent black smoke as high as possible to facilitate dissipation above the roadway.

Larry Koepke

San Jose

A The problem is when a blinding black cloud is pouring out of these modified exhaust pipes.

Q The pickup that was belching that awful smoke was not doing so because the exhaust pipe projected vertically between the cab and the bed. It did so because the engine is in serious need of a rebuild, tuneup or catalytic converter. Had the exhaust pipe come out at the rear under the bed the smoke would have been as black and noxious.

Dan Pitt

Palo Alto

A And ...

Q It is probably a very poorly tuned diesel engine that was making all the black smoke. Possible but less likely: an older gas engine with a carburetor problem. Either way, the advice to report is still good. If the smoke was bad enough to make cars brake and swerve, a call directly to the Highway Patrol would be warranted.

Eric Bernhard

A That's the issue I have. There was so much smoke spewing out that it posed a safety risk as drivers dodged into other lanes to avoid a large cloud of smoke near ground level.

Q Years ago, citizens band radios were very popular. Does the ban on cellphone use also affect the use of CBs while driving? And sometimes when we drive in a caravan, we'd use walkie-talkies to stay in touch with other cars. Is it still legal to use them in place of using cellphones?

Danny Lau

Cupertino

A Both CBs and walkie-talkies remain legal to use, says the CHP.

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