Some names to keep in mind are:
Old Pali Carriage road - built by the ancient Hawaiians as a foot path, dangerous, with some vertical rope climbs. It was used to transport taro, rice, butter from Kailua to Honolulu. In 1795, King Kamehameha defeated the O'ahu Hawaiians to consolidate his rule over all the islands. 400 warriers were forced off the mountain to their deaths at the Pali (cliffs) Lookout.
Old Pali Road - essentially a gradual improvement of the Carriage Road, done over the course of a couple of hundered years, culminating in 1887 with major work done by blasting powder and dynamite. Still, some of the grades were 49 degrees. The Old Pali Road was closed in the early 60s when the New Pali Road was finished.
New Pali Road - a highway with tunnels, completed in 1959, removing the incredible grades found on the old road.
Ancient Hawaiians built this "road" with stones set in the never-ending mud so they could climb, on foot, over the Pali Mountains from Kailua to Honolulu, carrying their taro, butter and rice to market. There were places on their trail which could only be traversed by a rope ladder. Can you imagine? We started this hike in awe of the daring and enterprising Hawaiians of long ago.
Transportation changed over time, from this being the footpath, to becoming a carriage road, though we can't imagine how carriage wheels went over this stuff, and at grades of up to 49 degrees!