Complex sentence: As technology improved, travelers no longer needed to stop as often for rest and supplies--by the 1980s travelers could easily travel from Los Angeles to locations in the Eastern Sierras with little more than brief stops for gas.
Split into simpler sentences: As technology improved, travelers no longer needed to stop as often for rest and supplies. By the 1980s travelers could easily travel from Los Angeles to locations in the Eastern Sierras with little more than brief stops for gas.