‘Bump Meter’ Gives Caltrans a Feel for the Worst Freeways

As every frustrated motorist knows, there are millions of jerks out there on the freeways--and that does not even include the kind who follow too closely or change lanes without warning.

Because of deteriorating pavement, each day drivers in the San Fernando Valley encounter a multitude of jerks, bumps, lurches and jolts while cruising the freeways.

A tour of three Valley freeways last week in a Caltrans car equipped with a “bump meter” uncovered long stretches of silky-smooth freeway interspersed with sections that seem like medieval cobblestone paths.

Bone-Jarring Stretch

It also encountered five stretches of pavement that failed to meet Caltrans’ standard for ride comfort--including a bone-jarring section of the Ventura Freeway in Woodland Hills that raised eyebrows among Caltrans engineers.

The ride provided a preview of a survey that California Department of Transportation crews will take next month of all Valley and Ventura County freeways as part of a statewide survey that has been conducted by Caltrans every two years since 1968. It includes riding each lane of freeway with one of six bump-meter equipped cars and visually inspecting each lane at various intervals.

Results are used to determine which areas need resurfacing or reconstruction.

The bump meter is a computer-like device with a probe attached to the car’s rear axle that records the shock transmitted to the auto by pavement cracks, potholes, raised chunks of roadway--even by pavement grooves designed to carry water away.

The meter spits out a tape similar to cashier’s. It provides a ride score that generally ranges from 0 to 100. The higher the score, the worse the road.

James Knox, Caltrans maintenance chief for Southern California, said that scores of 100 are rare and that the department fixes anything that registers over 45.

Among Valley problem areas, Chalk Hill, the 300-foot hill along the Ventura Freeway between Winnetka and De Soto avenues, was in a class by itself.

‘Awfully High’ Ratings

The westbound slow lane--the lane farthest to the right and almost always the bumpiest lane--recorded a bone-shaking 57.

The meter registered an 82 as the Caltrans car bounced down the hill eastbound in the slow lane.

Knox called the rating “awfully high, terribly high.”

Caltrans driver Vera Dolansky, who has been surveying California highways and freeways for several years, said it was not the highest rating she had encountered, “but it was right up there.”

At the other end of the Valley, on the northbound Golden State Freeway in Burbank, the meter registered a 51 in the slow lane just south of the Verdugo Avenue overpass.

Even that relatively smooth stretch of problem pavement made Caltrans’ American Motors Concord rattle, vibrate and thud.

Dolansky, a civil engineer, attributed the bumps to a process called “faulting,” which occurs when individual concrete slabs tilt. When that happens, motorists experience a thud as a vehicle’s wheels encounter each tilted slab.

Faulting most often occurs in the slow lane and is attributable to the weight of trucks, Dolansky said.

Smoother Pavement

Farther north on the Golden State, the pavement smoothed out rapidly.

At Magnolia Boulevard, as Dolansky maneuvered her vehicle between a gasoline tanker and tractor-trailer laden with gravel, the meter recorded 32, the result of what Dolansky said was mild faulting.

By Burbank Boulevard, the road had settled down to a 25. It maintained that level past Hollywood Way. By the Sunland Boulevard exit, the pavement was registering a ribbon-smooth 21, which it maintained for several miles.

The northbound Hollywood Freeway through North Hollywood had neither of the extremes of smoothness or bumpiness found on the Golden State Freeway in Burbank.

No Extremes

North of Magnolia Boulevard, the slow lane seldom exceeded 32 and only occasionally dropped below 28.

By contrast, the westbound Ventura Freeway west of the San Diego Freeway only occasionally registered as low as 32, and then only for brief sections between Hayvenhurst Avenue and Reseda Boulevard.

By the time the Caltrans meter car reached the Chalk Hill washboard section west of Winnetka, scores in the 30s were only a memory.

In addition to the 57 recorded on the hill, the westbound slow lane just west of Topanga Canyon Boulevard registered a 68.

Settles Down

By Woodlake Avenue, the roadway had settled down to a still-bumpy 62. By Valley Circle Boulevard, the meter reading was down to 52.

Not until Dolansky crossed into Calabasas did the ride score drop to 41, within the range deemed acceptable by Caltrans.

Eastbound, the freeway’s slow lane registered similar bumpiness levels, with the exception of the 82 reading on Chalk Hill.

But relief is not far away. Next year, Caltrans is scheduled to begin a $12.3 million rehabilitation project from Valley Circle Boulevard to Tampa Avenue.

Textbook Pavement

In its existing condition, Dolansky said the Ventura Freeway in the West Valley could serve as a textbook for teaching pavement analysis.

In addition to extensive faulting, almost every other ill known to highway engineers is present in abundance.

There are extensive sections of what road analysts call “alligator A” cracking--long, irregular splits in the pavement that resemble an alligator’s skin.

Many stretches have progressed to “alligator B” cracks, Dolansky said, in which shorter cracks join the original long ones.

“Potholes are the next step after alligator B cracks,” she said.

Evidence of ‘Pumping’

Dolansky said concrete sections in the West Valley exhibit widespread evidence of “pumping,” a highway engineer’s term for the telltale deposits of sand surrounding concrete cracks.

After the concrete cracks, usually from the weight of trucks, water seeps below, she said. Then the water, and some sand, is “pumped” up by the weight of traffic.

Caltrans spokeswoman Felicia Archer said faulting is usually corrected at night by grinding the edges of adjacent slabs to match.

Crack sealing, however, is accomplished in daylight, usually between 9 a.m. and 3 p.m., she said, “and inconveniences people and generates lots of telephone and written complaints to Caltrans.”