Primary, alternate and emergency routes only give you three chances if they leave in different directions and share no chokepoint, because a threat that blocks one bearing blocks every route near it. Space three routes about 120° apart and no threat narrower than 120° can block two of them; then choose the route whose bearing is farthest from the threat.
Part of Escape Route Planning
Primary, alternate and emergency routes are the three planned paths out of a site, ranked by speed and safety, which must diverge in direction and in the ground they cross so that one event cannot close them all.
Different Directions Are Worth Nothing If They Meet At A Bridge
The parent article sets the rule: a primary route that is your best and fastest, an alternate that goes a completely different direction and path, and an emergency route that is a last resort, possibly harder or more dangerous. They diverge from your location in different directions, because if all three go north, a threat from the north blocks all of them.
Direction is not the whole test. Routes that start in different directions but cross the same bridge, ford or pass are one route as far as a blocking force is concerned. The phase-0 article on escape routes calls these choke points: bridges, mountain passes, narrow valleys and tunnels (Escape Routes).
What You Need
- A map with compass bearings for the first leg of each route.
- A list of choke points on each route: bridges, fords, passes, narrow roads.
- The threat bearings from your threat assessment: where trouble is most likely to come from.
- A rule for choosing between routes on the day.
Method: Spread, Check For Shared Chokepoints, Pick
Step 1: Take bearings. Measure the compass bearing at which each route leaves the site.
Step 2: Spread them. With three routes aim at about 120° between neighbours. With two, aim at about 180°.
Step 3: List the choke points on each and check that no two routes share one. If they do, move one of the routes or find a different crossing.
Step 4: Decide which route to use by comparing the threat’s bearing with each route’s.
Step 5: Check that the alternate and emergency routes are still open at the start of each season.
Worked Example: Which Route, And How Wide A Threat Blocks Two
Spacing. Three routes leave at bearings 0° (north), 120° and 240°. A threat covering an arc of width w degrees can block two routes only if the arc includes both, and the closest two routes are 120° apart. So any threat narrower than 120° blocks at most one. If instead the routes leave at 0°, 30° and 60°, an arc of 60° blocks all three.
Choosing. A threat is reported at bearing 20°. The angular differences are: route 0° differs by 20°; route 120° differs by |120 - 20| = 100°; route 240° differs by |240 - 20| = 220°, and the smaller way round is 360 - 220 = 140°. Use the route with the largest difference, the 240° route (140° from the threat). The step also has to check that route’s choke points, because a bearing that looks away from the threat can curve back toward it.
Common Mistakes
- Three routes through one gate. They leave in different directions only after the gate; the gate is a choke point.
- Routes that merge ahead. They share the last leg and so share the risk.
- Choosing by speed on the day. Decide by the threat’s bearing, as above, in advance.
- An emergency route nobody has walked. The parent article wants everyone to walk each route at least twice.
Safety
The household's own fences and gates close routes too
A route that leaves through a locked gate, a hedge or a ditch you built is blocked by your own barrier, in a fire or an attack alike. Give each route an opening that opens from inside without a key and check it is clear. Rehearse at least one route in the dark. A route that crosses a river or a steep slope is dangerous in flood, ice or night.
What’s Next
- Learn next: Terrain Selection — choosing the ground each route crosses
- Combine with: Rally Points — where the group meets on each route