DEL MAR — After being reminded that the North Torrey Pines Bridge is considered one of the worst in the state as far as its ability to withstand an earthquake, Del Mar council members voted unanimously to allow an exemption to the city’s noise ordinance permitting night and weekend construction for a seismic retrofit and rehabilitation.

The city code allows exemptions for emergencies. “With all the studies that have recently come up about the anticipation of new seismic activity in California, I think it is an emergency,” Brian Mooney, interim planning director, said. “(Based on) all the technical evidence we’ve seen, if there is substantial seismic activity, this bridge would be susceptible to failure.”

The project is expected to require work on 70 to 100 nights and some weekends during the next three years. Nighttime work will occur, on average, once every two weeks, although there may be an occasional need for construction on two or three consecutive nights, said Jason Reynolds, project manager from EDAW, an architectural and environmental consulting company working on the project. The number of weekends will be partially dictated by North County Transit District, he said.

Although most work can be done during the day, construction over the railroad tracks and on the road must be done at night. “(According to) railroad laws and the railroad safety union, you can’t work with machinery over the railroad tracks when there’s going to be trains,” James Kurtz, an EDAW noise engineer, said.

“In order to have the job progress, you have to work during the periods when the trains aren’t running,” Kurtz said. “In the same way, you can’t lift the slabs off the top of the bridge during the day. You don’t want to close the road in the middle of the day.”

Equipment used will include cranes, generators, loaders and chippers. Diesel engines will be the dominant source of noise. Residents will also hear backup alarms, but Kurtz said alarms used at night aren’t quite as loud as those used during the day.

“The noise will be discernable,” Reynolds said. “You’ll hear it, but it will not be intrusive.”

The contractor will be required to submit a noise abatement plan to the city for review. There will be performance measures and nighttime monitoring. If predicted attainable noise levels are not being met, construction can be halted until a remedy is found, Reynolds said.

Notices stating when work will occur will be sent to homes within 1,200 feet of the site at least one month before the project starts. The city may also create a hot line residents can call for construction updates.

Council members said they were satisfied with the steps being taken to minimize noise.

“I’m very impressed with the measures that are being taken,” Councilman Henry Abarbanel said. “I was actually quite worried that there would be a lot of low-frequency sound from the diesel engines, and I’m reassured that there (will) not be.”

“We will still have people complain,” Mayor Dave Druker said. “But ultimately, just like the bluffs had to be done, this has to be done.”

“I’m always concerned when government wants to suspend its own rules for its own purposes,” Councilman Richard Earnest said. “But given the conversation this evening, I’m comfortable that we really don’t have a choice in this case. It is for the public safety and it is our responsibility to look after that, so I am much comforted by that and by the analysis of what’s being done to mitigate these things.”

According to the staff report, the alternative to nighttime construction is a longer completion time, which would have a more significant adverse effect on the environment. In addition to making the bridge safer, the retrofit will increase its life expectancy to approximately 75 years.