According to Gachagua, the project has stalled because the alleged payment was expected upfront in cash from the China Road and Bridge Corporation (CRBC).
He claimed the Chinese firm is insisting on being awarded the contract first before releasing any money.
The former Deputy President argued that the continued delay in the multibillion-shilling road project has raised serious concerns about transparency and accountability in the government’s handling of major infrastructure deals.
The Rironi-Mau Summit highway has been viewed as a key project expected to ease traffic congestion along the busy Nairobi-Nakuru route and improve transport between Nairobi and western Kenya.
Gachagua’s claims are likely to intensify political debate surrounding government procurement processes and foreign-funded infrastructure projects.