The men in charge of the work wear the uniform of the HVO. The Croatian Defence Council is the military arm of the recently proclaimed Croatian state-within-a-state in Bosnia, called Herceg Bosna.
When the road is finished, the Croatians will be able within a few hours to transport food and arms from the port of Split across 150 miles of what was an impassable mountain range to Kiseljak, the last Croatian-held town before Sarajevo.
Many of the 300,000 inhabitants in Sarajevo, now entering a fourth month under Serbian blockade and bombardment, look to the Croatian forces poised on the edge of the city at Kiseljak as potential liberators.
The briefest look at the state of play round Kiseljak suggests they are victims of a delusion.
Between the Croatian flagpole at Kiseljak and the Serbian flagpole at Ilidza, on the outskirts of Sarajevo, not one bullet has been fired during four months of war in Bosnia.
I saw no open fraternisation between two lightly armed Serbian policemen in Ilidza and their Croatian counterparts a few miles down the road in Kiseljak. But when the Serbian police casually offered me a police-car escort all the way to the first Croatian position, I realised this was not a frontline but a frontier.
Between Kiseljak and Ilidza runs the new border between Croatia and Serbia. And very peaceful it is. Only it runs right outside Sarajevo. And no Muslims on either side of the new 'frontier' have been consulted.
No Serbian grenades have fallen on Kiseljak. It is only a few minutes away from the blackened and bombed-out facades of Sarajevo, where the hospitals are full of wounded and the shops are empty, where teenage Muslim fighters take out Serbian tanks with ancient machine guns, where women fight with their fists for a United Nations food parcel.
But in Kiseljak life ticks by in a kind of rural idyll. The grocery shops are laden with bunches of bananas and trays of oranges. Pensioners sit chatting in the sun. The village priest cycles past, doing his parochial rounds.
Croatian officials angrily rebut the accusation of joining the Serbians in a Bosnian carve-up. They point out that the new Croatian zone has not seceded from Sarajevo and that thousands of Muslims in flight from Serbian 'ethnic cleansing' have found sanctuary in Herceg Bosna.
In Croat-held Jablanica and Konjic, I saw thousands of refugees from the east, many dressed in their traditional colourful baggy trousers, making makeshift homes for themselves in former army barracks.
But there is no question who runs the show in Herceg Bosna. The red-and-white Croatian chequerboard is more often seen these days than the Bosnian fleur-de-lis. And Mate Boban, the President of Herceg Bosna, has described the region as 'Croatian land.' In an interview, he said: 'Whatever the people in Sarajevo do is their personal business. They cannot speak or decide a thing in the name of the people of Herceg Bosna.'
His deputy, Jozo Maric, was harsher. 'We don't recognise the Bosnian flag, the Bosnian presidency or a unifed Bosnian army. They don't have an army in Sarajevo. How can they expect us to place our forces under their control?'
One of Mr Boban's first acts as President of Herceg Bosna was to scrap all the Territorial Defence units loyal to Sarajevo in his domains and proclaim the local Croatian militia the only permitted armed force.
No Muslims have been removed from local government but no Muslims have been included in the government of Herceg Bosna either. The message is that Muslims are welcome as soldiers or officials, but on 'Croatian land' they will never be more than useful tenants.
If I were a Muslim, I would certainly prefer playing second fiddle to the Croatians in cosy Kiseljak to being killed by the Serbians in eastern Bosnia. But either way Bosnia is disappearing and dying, set on fire and uprooted by the Serbians in eastern Bosnia, painlessly snuffed out by the Croatians in the south west. The old Bosnia, the ethnic mosaic of Croatians, Serbians and Muslims has shrunk to a few square miles inside Sarajevo.
Clinging on grimly inside Sarajevo, the Bosnian forces still look hopefully towards the hills rising to the west of the city, where Croatian forces are entrenched. Little do they know, however, that help from that direction will probably never come.Reuse content