This is what the half-tunnel in Bonglo, Atok, Benguet looked like many years ago before the road was paved and before the construction of concrete parapets as a safety measure.
This section of the Halsema Highway is a popular stopover for motorists and travellers. It was carved out of solid rock. Construction of the Halsema Highway started in 1922 under then Baguio City mayor Eusebius Halsema. It's now the most important highway in the Cordillera region.
However, the half-tunnel was carved out only in the 1960s when Typhoon Trining washed out this section of the road. Two mining companies whose operations were heavily affected by the closed road decided to collaborate to help reopen the road.
The whole story about the carving of the half-tunnel and reopening of Halsema Highway is best described by Rufino Bomasang who left a comment when we previously posted about the half-tunnel.
Here's his comment in full:
"This portion of the Halsema Road was completely washed out by Typhoon Trining in the late 1960s (actually in October 1967). I know this for a fact because I was then Project Superintendent of the Boneng Copper Project in Atok, Benguet under Itogon-Suyoc Mines, Inc (ISMI) and we were monitoring what was happening because the road was closed for weeks and Suyoc Mine and Lepanto mine, both in Mankayan, Benguet were isolated. The two mining companies then agreed to cooperate to reopen Halsema Road with Lepanto clearing all the slides from Mankayan all the way to the washed out portion in Atok, while ISMI would drive a half tunnel through the washed out portion. Thus, Eng’r. Godofredo Acosta of ISMI (who was formerly my Assistant at Boneng but reassigned to Itogon) was assigned as Project Engineer and under him was a crew of mostly Igorot miners from Itogon headed by Mr. Omero, Mine Foreman of ISMI. According to Eng’r Acosta, the driving of the half tunnel was completed by his crew from ISMI without the involvement of Lepanto, whose crew was concentrating on clearing the slides all the way to Mankayan."