Route Planning

Part of Roads and Transport

How to plan an optimal road route between two points, balancing distance, terrain, drainage, and construction cost.

Why This Matters

A road built on the wrong route is worse than no road at all. It consumes enormous labor, produces a surface that floods or erodes repeatedly, and commits your community to that bad route for generations — because once a road exists, land uses develop around it, making it politically and economically difficult to abandon even when it is clearly inferior.

Route planning done well before construction begins identifies the path that minimizes construction cost, minimizes ongoing maintenance, maximizes load capacity for all seasons, and can be defended (in the military sense) or expanded as the community grows. Poor route planning gives you a road that floods every spring, requires constant regrading, cannot handle heavy loads after rain, and forces loaded vehicles onto a switchback route that adds an hour to every journey.

The principles of route planning were developed empirically over millennia of road building. Roman road engineers walked the terrain for days before committing to a route. Medieval road commissioners consulted local farmers and drovers who had walked the ground for generations. Modern survey techniques formalize what experienced route planners knew intuitively.

Step 1: Define the Requirements

Before walking any ground, write down what you need from the road.

Questions to answer:

• What are the two (or more) endpoints?
• What is the expected traffic volume? (Foot traffic only, pack animals, wheeled vehicles, heavy wagons?)
• What is the heaviest expected load? (A heavy wagon loaded with stone sets completely different requirements than a foot path carrying people with packs.)
• What seasons must the road be usable? (All-weather versus dry-season-only dramatically changes design requirements.)
• What are the time constraints? (Is this route critical for the upcoming harvest, or is it a long-term project?)
• What materials and labor are available?

These answers define your design standard. A footpath to a water source needs only clearing. A road carrying grain wagons to market needs drainage and a gravel surface. A road that must carry stone blocks for building needs Roman-level construction.

Step 2: Map-Level Analysis

Before walking the terrain, gather information at a map scale.

If you can make a sketch map:

1. Mark all known obstacles: rivers, marshes, steep ridges, cliffs, dense forests
2. Mark all known resources: gravel deposits, stone outcrops, water sources for construction
3. Mark existing trails, paths, or roads (even poor ones — they indicate where people have already found the easiest way)
4. Mark the highest points and lowest points between your endpoints

Identify the key decision points:

• Every river or stream crossing: can it be forded? Bridged? Where is the best crossing point?
• Every steep ridge: can it be avoided? Must it be crossed? Where is the lowest saddle?
• Every wetland: can it be skirted? How far does the detour add?

Preliminary route options: Draw two or three possible routes on the sketch map, each taking a different approach to the major obstacles. These will be evaluated on the ground.

Step 3: Field Reconnaissance

Walk all preliminary routes, ideally with someone who knows the ground.

What to observe and record for each route:

Terrain and slope:

• Locate all significant grade changes. Walk with a simple level (a tube of water) or a clinometer (a weighted string on a protractor)
• Record the maximum grade on each route option. Remember: loaded vehicles cannot exceed 8-10% grade sustainably; 5% is the comfortable maximum
• Note the total elevation change (more change = more animal effort over the full route)

Drainage and water:

• Walk after rain if possible. Water does not lie — wet ground shows exactly where drainage problems exist
• Count every stream crossing and note the flood stage evidence (high water marks on banks, flood-deposited debris in trees)
• Note areas of standing water, saturated soil, or springs
• Note where natural water flow crosses your proposed route — each crossing needs a culvert

Ground conditions:

• Test the soil bearing capacity by probing with a steel rod or pointed stick. A probe that sinks easily indicates soft ground requiring special treatment.
• Note rock outcrops (potential cutting required but provides free stone) and gravel deposits (free base material)
• Note areas of dark, spongy soil (organic material — avoid or excavate completely)

Existing infrastructure:

• Note any existing culverts, bridges, or improved crossings that could be incorporated
• Identify any sections of existing track that could be improved rather than replaced

Ask Local Knowledge

Farmers, hunters, and livestock herders who have used the terrain for years know where the bogs are in spring, where the stream floods, where the soft ground is, and where the game trails run (animals find natural efficient routes). This knowledge is invaluable and faster to gather than any surveying.

Step 4: Grade Analysis

For each route option, calculate the grade profile and compare.

Simple grade measurement:

1. Set two ranging poles (straight sticks) vertically in the ground, 20-30 paces apart on a slope
2. Sight a level string or rope between the poles (use a water level to ensure it is horizontal)
3. Measure the height of the uphill pole from ground to string, and the downhill pole from ground to string
4. The difference in heights divided by the horizontal distance is the grade
5. Example: uphill pole height 180 cm, downhill pole height 80 cm, distance 20 m. Grade = (180-80) cm / 2000 cm = 5%

Maximum acceptable grades:

Vehicle Type	Maximum Grade	Comfortable Grade
Foot and pack animals	15-20%	10%
Unladen wagon	10-12%	8%
Loaded wagon (moderate)	7-8%	5%
Heavily loaded wagon	5%	3-4%

Route comparison: If Route A has a maximum grade of 4% but is 15 km longer than Route B with a maximum grade of 8%, calculate the loaded travel time for each. A slower-climbing team that can maintain full load often wins over a shorter route that requires reducing loads or double-tripping.

Step 5: Comparing Route Options

Create a comparison table for all route options.

Factor	Route A	Route B	Route C
Total length (km)
Maximum grade (%)
Number of stream crossings
Length through soft/wet ground
Available stone/gravel en route
Estimated construction labor (person-days)
Estimated annual maintenance (person-days)
All-weather usability

Scoring: Weight these factors according to your requirements. If all-weather use is critical, weight that heavily. If construction labor is very limited, minimize construction cost.

Step 6: Switchbacks for Steep Terrain

When no route avoids a steep grade, switchbacks (zigzag routes up a slope) reduce the effective gradient at the cost of added distance.

Switchback design:

• Each switchback adds distance but reduces grade. The relationship is direct: doubling the length halves the grade.
• For loaded wagon traffic, the switchback turns must be wide enough for a wagon to make the turn without jackknifing. Minimum turning radius for a typical two-horse wagon: 8-10 meters from the inside wheel.
• The switchback platform (the flat area where the vehicle turns) must be level enough that the wagon does not tip while turning. If the hillside slopes more than 3-4%, cut the platform into the hill.
• Reinforce the outer edge of each switchback with stone retaining walls — this is the highest stress point in the design and the first to fail.

When to use switchbacks: Only when a straight route would require a grade over 8-10% for a significant distance (more than 100 meters). A single short steep section can be managed with extra animals or rope-assisted hauling for the steep section.

Step 7: Documentation

After selecting the final route, document it thoroughly before breaking ground.

Route documentation includes:

1. A sketch plan showing the entire route with distances, grade locations, crossing locations, and major features
2. Notes on any special construction requirements at each problem section
3. An estimate of materials required (total length times standard construction quantities)
4. An estimate of labor required by phase (clearing, grading, drainage, base, surface)
5. A priority sequence: if resources run out, which sections get finished first?

This documentation serves as the construction plan and is invaluable if construction happens over multiple seasons.