class Road
{
(…)

	_min_distance = AIMap.GetMapSizeX() + AIMap.GetMapSizeY();

	constructor
	{
	(…)
	}

	function InitializePath(sources, goals) {
		local nsources = [];

		foreach (node in sources) {
			nsources.push([node, 0xFF]);
			foreach (tile in goals) {
				_min_distance = min(_min_distance, AIMap.DistanceManhattan(node, tile));
			}
		}
		this._pathfinder.InitializePath(nsources, goals);
	}
	(…)
}

function Road::_Estimate(self, cur_tile, cur_direction, goal_tiles,
		_AIMap = AIMap)
{
	local min_cost = self._max_cost;
//	/* As estimate we multiply the lowest possible cost for a single tile
//	 * with the minimum number of tiles we need to traverse. */
	foreach (tile in goal_tiles) {
		local distance = _AIMap.DistanceManhattan(cur_tile, tile);
		if (distance > self._min_distance) {
			distance += distance - self._min_distance;
		}
		min_cost = min(distance * self._cost_tile, min_cost);
	}
	return min_cost;
}