Travel Speed Reference¶

This page provides detailed information about how SocialMapper assigns travel speeds for accurate isochrone generation.

Overview¶

SocialMapper uses OSMnx 2.0's sophisticated speed assignment system to calculate realistic travel times. The system considers both real-world speed limit data from OpenStreetMap and intelligent fallbacks based on road types and travel modes.

Speed Assignment Hierarchy¶

When generating isochrones, OSMnx assigns edge speeds using this priority order:

OSM maxspeed tags - Uses actual speed limits from OpenStreetMap data when available
Highway-type speeds - Falls back to our configured speeds for each road type
Statistical imputation - For unmapped highway types, uses the mean speed of similar roads in the network
Mode-specific fallback - As a last resort, uses the travel mode's default speed

Travel Mode Speeds¶

Driving Mode¶

Default fallback speed: 50 km/h (31 mph)

Highway Type	Speed (km/h)	Speed (mph)	Description
motorway	110	68	Highways/freeways
motorway_link	70	43	Highway on/off ramps
trunk	90	56	Major arterial roads
trunk_link	50	31	Major road ramps
primary	65	40	Primary roads
primary_link	40	25	Primary road connectors
secondary	55	34	Secondary roads
secondary_link	35	22	Secondary road connectors
tertiary	45	28	Local connector roads
tertiary_link	30	19	Tertiary road connectors
residential	30	19	Neighborhood streets
living_street	20	12	Shared residential spaces
service	25	16	Service/access roads
unclassified	40	25	Unclassified roads
road	40	25	Unknown road types

Walking Mode¶

Default fallback speed: 5 km/h (3.1 mph)

Path Type	Speed (km/h)	Speed (mph)	Description
footway	5.0	3.1	Dedicated pedestrian paths
sidewalk	5.0	3.1	Sidewalks along roads
pedestrian	5.0	3.1	Pedestrian areas
residential	4.8	3.0	Residential streets (may lack sidewalks)
tertiary	4.8	3.0	Less busy roads
path	4.5	2.8	General paths (may be rough)
living_street	4.5	2.8	Shared spaces, need caution
service	4.5	2.8	Service roads
primary	4.5	2.8	Busy roads may slow walking
secondary	4.5	2.8	Busy roads
trunk	4.0	2.5	Very busy roads, often no sidewalk
motorway	3.0	1.9	Highways (rarely walkable)
steps	1.5	0.9	Stairs are very slow

Biking Mode¶

Default fallback speed: 15 km/h (9.3 mph)

Path Type	Speed (km/h)	Speed (mph)	Description
primary	20.0	12.4	Good roads, higher speeds
cycleway	18.0	11.2	Dedicated bike lanes
secondary	18.0	11.2	Moderate traffic
tertiary	16.0	9.9	Light traffic
residential	15.0	9.3	Residential streets
trunk	15.0	9.3	May be dangerous/restricted
path	12.0	7.5	Shared paths
service	12.0	7.5	Service roads
living_street	10.0	6.2	Shared spaces
motorway	10.0	6.2	Highways (if allowed)
footway	8.0	5.0	Shared with pedestrians
pedestrian	8.0	5.0	Pedestrian areas

Implementation Details¶

Code Example¶

Here's how travel speeds are applied during network processing:

from socialmapper.isochrone.travel_modes import (
    TravelMode, 
    get_highway_speeds,
    get_default_speed
)
import osmnx as ox

# Get mode-specific configuration
travel_mode = TravelMode.DRIVE
highway_speeds = get_highway_speeds(travel_mode)
fallback_speed = get_default_speed(travel_mode)

# Download and process network
G = ox.graph_from_point(
    (latitude, longitude),
    network_type="drive",
    dist=5000
)

# Apply speeds with OSMnx 2.0's intelligent assignment
G = ox.add_edge_speeds(
    G, 
    hwy_speeds=highway_speeds,  # Our highway-type speeds
    fallback=fallback_speed     # Last resort fallback
)
G = ox.add_edge_travel_times(G)

Speed Data Quality¶

The accuracy of isochrone boundaries depends on the quality of OpenStreetMap data in your area:

Areas with good coverage: Most edges will have actual speed limits, resulting in highly accurate isochrones
Areas with sparse coverage: The system falls back to highway-type speeds, which still provide reasonable estimates
Rural or unmapped areas: May rely more heavily on statistical imputation and fallback speeds

Customizing Speeds¶

While SocialMapper's default speeds are based on typical real-world conditions, you may need to adjust them for specific use cases:

Urban congestion: Reduce speeds during peak hours
Rural areas: May have higher actual speeds than defaults
Special conditions: Weather, construction, or events affecting travel

Currently, speed customization requires modifying the source code in socialmapper/isochrone/travel_modes.py.

Speed Validation¶

SocialMapper enforces speed limits for each travel mode:

Mode	Minimum Speed	Maximum Speed
Walk	3.0 km/h (1.9 mph)	7.0 km/h (4.3 mph)
Bike	8.0 km/h (5.0 mph)	30.0 km/h (18.6 mph)
Drive	20.0 km/h (12.4 mph)	130.0 km/h (80.8 mph)

These limits prevent unrealistic speed assignments that could distort isochrone boundaries.