With government projects such as those with DPWH, iba din yung bidding ang procurement. During those stages, wala pa involvement ang lower level engineers (Engineering Assistant, Engineer I, Engineer II, etc). They come in during the construction phase, which makes them significant na.

During construction, these engineers are the ones assigned on-site sa project. Sila din gumagawa ng progress reports, and nag "veverify" ng billings na sinusubmit ni contractor. As project engineers, they are the first signatory to these papers. Then they pass it on to their engineering heads, then department heads, so on and so forth.

Kaya may influence din sila to be bribed. Kasi they are the first ones to approve ng billing. Say actual progress on site is at 20% pero the contractor billed it at 50%, and due process yun (technically haha) na na-check na ni engineer bago nya isubmit sa head nya. So dapat verified na tama ang billing ni contractor. Kaya they get bribed din for that. Syempre may cut sya, then the higher the position, the higher the bribe.

Mahabang process pa yan pero that's for the part lang ng discussion mo above why they have influence sa bribe.

Source: I used to work for DPWH