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Carmel Valley’s a traditionally suburban community. The master-planned community from the 1970s is part is within the boundaries of the city of San Diego but it’s 20 miles from downtown, isn’t well served by public transportation and most residents park their cars out front of their single-family homes.

That’s both the selling point and the opposition to One Paseo, a proposed development of homes, offices, stores, restaurants and outdoor space spread across 23 acres at the corner of Del Mar Heights Road and El Camino Real.

Kilroy Realty, the project’s developer, has sold the 1.4 million square feet project of new buildings and 600 housing units as “A Main Street for Carmel Valley,” promising outdoor promenades between desired grocer stores and movie theaters – a setting that would let new residents live, work and play in the same place.

Opponents have seized on that very framing. They’ve named their group “What Price Main Street?” That opposition has made the case that the biggest toll the project will take on Carmel Valley residents will come in the form of deadlocked traffic.

The idea that traffic will be dramatically delayed as a result of One Paseo has basically become accepted as fact, to the point that residents in nearby Torrey Pines now fret that they, too, could be impacted if ambulances responding to emergencies in their community are slowed by clogged roads.

Getting a grasp of exactly how much traffic the project will add, and just how much of an impact it will have on daily life in the area isn’t easy.

It’s been studied, extensively, in the required report on the project’s environmental impact, but nearly every conclusion comes with a list of caveats or confounding factors that prevent a straight answer.

That was the basis for one of the major events that got the project to this point: the Carmel Valley Community Planning Board asked city traffic engineers to simply tell them what the affect on traffic would be.

By all accounts, the board’s members and residents walked away with more questions than they had before.

Let’s take a step back. How much traffic will the project generate?

Well, the developer’s original proposal to build 1.8 million square feet of usable space, per the environmental report, would add 26,961 trips to the area every day. The new proposal, scaled down to 1.4 million square feet, would add 23,854 trips each day.

That’s three times the total trips that would be generated by the project that’s already approved to be built on the 23-acre parcel. That project – a 500,000 square foot office space – would produce 6,500 daily trips.

(The existing community plan for the area has zoned the property for 500,000 square feet of office space. Kilroy, after purchasing that lot, is asking to change the plan so it can build its 1.4 million square foot project. The City Council has final say over that request, but not until the local planning group and citywide Planning Commission weigh in with their recommendations.)

So the traffic at the heart of the opposition’s case is basically the difference between the 6,500 trips that the developer could add to the area without having to ask anyone’s permission, and the 23,854 trips its larger project would add.

How big a deal is adding 17,200 car trips per day to a community like Carmel Valley?

“What you need to consider is (that number) is what the site will generate on average,” said Farah Mahzari, a city traffic engineer. “That’s not all going to come out at once … that’s not a good comparison. A peak comparison is what matters.”

Meaning: Traffic experts don’t think the number of cars that passes through an area over the course of the day is all that telling. More important is how many cars are coming through an area during morning and evening rush hour, when the volume is such that it could overwhelm a road or intersection or freeway on-ramp’s capacity.

Let’s look, then, at a single intersection as a representative sample of what One Paseo might do to traffic in the surrounding area.

Mahzari pointed me to a 2007 traffic count at the morning and evening rush hours for the intersection of Del Mar Heights Road and El Camino Real.

During each rush hour, something to the order of 4,200 cars head through the intersection, in either direction.

If the empty lot on the intersection’s southwest corner were to be built into 500,000 square feet of office space – the project that’s already approved, which would generate 6,500 trips per day – there’d be fewer than 200 additional cars going through the intersection during each rush hour, or a little less than a 5 percent increase in the total traffic flow.

In the case of the large One Paseo proposal, the 1.8 million square foot proposal that’s since been pared down, there’d be a 38 percent increase (1,632 cars) in cars coming through the intersection during morning rush hour. (Mahzari provided data on the since-abandoned 1.8 million square foot proposal because one for the smaller option isn’t available.)

In the afternoon rush hour, the 1.8 million square foot proposal would generate 33 percent of the current volume, or 1,398 new trips.

“Any of the other alternatives will be somewhere in between,” Mahzari said.

But because the new proposal requires a community plan amendment, Kilroy is responsible for providing investments in the area that’ll offset its impact on the community.

“The project applicant must identify feasible mitigation measures to bring the facility back to the level previously held prior to the project’s traffic impacts,” Mahzari wrote in an email.

At Del Mar Heights Road and El Camino Real, that’d mean widening the road to create a 365-foot eastbound right-turn, which the traffic report says will fully mitigate the project’s effects.

Bob Fuchs, with What Price Main Street, said the mitigation measures that brings the area back to its current service level wouldn’t be fully implemented until 2030, even though the study assumes the project will come on-line in 2016.

“The traffic study has a 14-year gap where you don’t know what you’ve got, or you have a bad situation,” he said. “It seems to me they’ve determined they’re not going to deal with that.”

Andrew Keatts

I'm Andrew Keatts, a managing editor for projects and investigations at Voice of San Diego. Please contact me if you'd like at

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