Complex sentence: Work began in 1963 to upgrade the highway between Coaldale and Barnwell so it could carry loads up to, and the final alignment for the upgraded highway through Barnwell had been confirmed by March 1966 with construction beginning shortly thereafter.
Split into simpler sentences: Work began in 1963 to upgrade the highway between Coaldale and Barnwell so it could carry loads up to. Upgrades continued through the decade, and the final alignment through Barnwell had been confirmed by March 1966, with construction beginning shortly thereafter.