Lilac Road Bridge: The story behind San Diego County's iconic arch bridge

Aug 19, 2025 - 17:00

BONSALL, Calif. (FOX 5/KUSI) -- If you're driving between North County and San Diego on Interstate 15, you're sure to recognize the arch bridge that hangs over the Escondido Freeway.

The iconic structure is one of San Diego County's most recognizable landmarks, but perhaps only few of its residents know it by name.

The Lilac Road Bridge, as its colloquially called, connects Bonsall from the west of I-15 to the communities of Lilac, Hidden Meadows and Valley Center to the east.

It spans about 700 feet long and suspends 150 feet over the I-15 traffic lanes, offering drivers a stunning view as they leave or enter into the city of Escondido.

The breathtaking piece of architecture was simply known as the West Lilac Road Overcrossing when it was built in 1978.

It was a part of a broader vision by Jacob Dekema, who was also known as "Mr. Caltrans" for his contributions to the region's transportation system and its intricate system of freeways and highways. Dekema served as the head of the San Diego office of Caltrans from 1955 to 1980.

According to the San Diego History Center, undertaking the Lilac Road project proved to be complicated for Caltrans engineers and contractors, as the geographical location and surrounding terrain came with various challenges.

Lilac Road Bridge over I-15 winding through Bonsall and north San Diego County. (Raquel Lonas/Getty Images)

Plus, the design of the bridge -- from its arch to its sloping girders -- were all asymmetrical, needing precise calculations to ensure the bridge would be structurally sound.

Before the bridge was built, the hill had a cut intended for the new I-15 lanes to travel through. Then, eleven million cubic yards of rock had to be excavated to ensure the bridge could be properly installed.

The Lilac Road Bridge took a total of nearly two years and $1.5 million to complete, according to the San Diego History Center.

Now, nearly five decades later, it stands as one of the lasting contributions made by the region's civil and structural engineers and as a gateway connecting different communities of San Diego County.