He was the key proponent for building the Carmel-San Simeon Highway along the Big Sur coast.

In 1897, he walked the entire stretch of rocky coast from Monterey to San Luis Obispo in five days and mapped out the course of the future road.

In 1915, he presented the results of his survey and photographic work to a joint session of the California legislature.

Roberts initially promoted the coastal highway to allow access to a region of spectacular beauty, but failed to obtain funding.

[1][3] The $1.5 million bond issue was approved by voters, but construction was delayed by World War I.