{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"stopping-distance"},"result":{"entity_type":"calculator","id":"stopping-distance","calculator_id":"stopping-distance","canonical_url":"https://tttkmbb.com/engineering/stopping-distance","name":"Stopping Distance Calculator","title":"Vehicle Stopping Distance Calculator – Reaction Distance plus Braking Distance from Speed, Reaction Time and Road Friction","category":"engineering","category_name":"Engineering & Automotive","tool_name":"calculate_stopping_distance","featured_mcp_tool":false,"description":"Computes the reaction (thinking) distance, braking distance and total stopping distance of a vehicle from its speed, the driver's reaction time and either a road-condition friction coefficient or a given deceleration, in metres and feet.","use_when":"You want to know how far a car travels before it stops from a given speed on dry, wet, snowy or icy roads, or the effect of reaction time.","do_not_use_when":"You need the deceleration itself from speeds and times (use acceleration), or the energy dissipated in braking (use kinetic-energy).","inputs":[{"name":"speed_km_h","label":"Speed","type":"number","unit":"km/h","required":true,"max":500,"exclusive_min":0,"description":"Initial vehicle speed in km/h (mph × 1.609344).","example":100},{"name":"reaction_time_s","label":"Reaction time","type":"number","unit":"s","required":false,"default":1.5,"min":0,"max":10,"description":"Perception–reaction time before the brakes act: 1.0–1.5 s alert driver, 2.5 s is the AASHTO road-design value.","example":1.5},{"name":"road_condition","label":"Road condition","type":"enum","required":false,"default":"dry","values":[{"value":"dry","label":"Dry asphalt (μ = 0.7)"},{"value":"wet","label":"Wet asphalt (μ = 0.4)"},{"value":"snow","label":"Packed snow (μ = 0.2)"},{"value":"ice","label":"Ice (μ = 0.1)"}],"description":"Typical tyre–road friction coefficient; overridden by friction_coefficient or deceleration_m_s2 when given.","example":"dry"},{"name":"friction_coefficient","label":"Friction coefficient μ","type":"number","required":false,"max":1.5,"exclusive_min":0,"description":"Optional custom coefficient of friction (deceleration = μ × 9.80665 m/s²)."},{"name":"deceleration_m_s2","label":"Deceleration","type":"number","unit":"m/s²","required":false,"max":20,"exclusive_min":0,"description":"Optional braking deceleration in m/s² (e.g. 3.4 for the AASHTO design value, 8–10 for a modern car with ABS on dry road); takes precedence over friction."}],"outputs":[{"name":"speed_m_s","label":"Speed","type":"number","unit":"m/s","decimals":4,"description":"speed_km_h / 3.6."},{"name":"deceleration_m_s2","label":"Deceleration used","type":"number","unit":"m/s²","decimals":4,"description":"μ × g or the given deceleration."},{"name":"reaction_distance_m","label":"Reaction distance","type":"number","unit":"m","decimals":2,"description":"Distance covered at constant speed during the reaction time: v × t_r."},{"name":"braking_distance_m","label":"Braking distance","type":"number","unit":"m","decimals":2,"description":"v² / (2 a)."},{"name":"total_stopping_distance_m","label":"Total stopping distance","type":"number","unit":"m","decimals":2,"description":"Reaction distance + braking distance."},{"name":"reaction_distance_ft","label":"Reaction distance","type":"number","unit":"ft","decimals":1,"description":"In feet (÷ 0.3048)."},{"name":"braking_distance_ft","label":"Braking distance","type":"number","unit":"ft","decimals":1,"description":"In feet."},{"name":"total_stopping_distance_ft","label":"Total stopping distance","type":"number","unit":"ft","decimals":1,"description":"In feet."},{"name":"braking_time_s","label":"Braking time","type":"number","unit":"s","decimals":3,"description":"v / a."},{"name":"total_time_s","label":"Total time to stop","type":"number","unit":"s","decimals":3,"description":"reaction_time_s + braking_time_s."}],"input_schema":{"type":"object","properties":{"speed_km_h":{"description":"Initial vehicle speed in km/h (mph × 1.609344). Unit: km/h.","type":"number","maximum":500,"exclusiveMinimum":0,"examples":[100],"x-unit":"km/h"},"reaction_time_s":{"description":"Perception–reaction time before the brakes act: 1.0–1.5 s alert driver, 2.5 s is the AASHTO road-design value. Unit: s.","type":"number","minimum":0,"maximum":10,"default":1.5,"examples":[1.5],"x-unit":"s"},"road_condition":{"description":"Typical tyre–road friction coefficient; overridden by friction_coefficient or deceleration_m_s2 when given.","type":"string","enum":["dry","wet","snow","ice"],"default":"dry","examples":["dry"]},"friction_coefficient":{"description":"Optional custom coefficient of friction (deceleration = μ × 9.80665 m/s²).","type":"number","maximum":1.5,"exclusiveMinimum":0},"deceleration_m_s2":{"description":"Optional braking deceleration in m/s² (e.g. 3.4 for the AASHTO design value, 8–10 for a modern car with ABS on dry road); takes precedence over friction. Unit: m/s².","type":"number","maximum":20,"exclusiveMinimum":0,"x-unit":"m/s²"}},"additionalProperties":false,"required":["speed_km_h"]},"output_schema":{"type":"object","properties":{"speed_m_s":{"description":"speed_km_h / 3.6. Unit: m/s.","type":"number","x-unit":"m/s"},"deceleration_m_s2":{"description":"μ × g or the given deceleration. Unit: m/s².","type":"number","x-unit":"m/s²"},"reaction_distance_m":{"description":"Distance covered at constant speed during the reaction time: v × t_r. Unit: m.","type":"number","x-unit":"m"},"braking_distance_m":{"description":"v² / (2 a). Unit: m.","type":"number","x-unit":"m"},"total_stopping_distance_m":{"description":"Reaction distance + braking distance. Unit: m.","type":"number","x-unit":"m"},"reaction_distance_ft":{"description":"In feet (÷ 0.3048). Unit: ft.","type":"number","x-unit":"ft"},"braking_distance_ft":{"description":"In feet. Unit: ft.","type":"number","x-unit":"ft"},"total_stopping_distance_ft":{"description":"In feet. Unit: ft.","type":"number","x-unit":"ft"},"braking_time_s":{"description":"v / a. Unit: s.","type":"number","x-unit":"s"},"total_time_s":{"description":"reaction_time_s + braking_time_s. Unit: s.","type":"number","x-unit":"s"}}},"formula":"v = speed_km_h / 3.6; a = μ × 9.80665 (or deceleration_m_s2); reaction_distance_m = v × reaction_time_s; braking_distance_m = v² / (2 a); total = reaction + braking; braking_time_s = v / a","method":"Constant-deceleration model on level road; braking distance grows with the square of speed. Friction values are typical (dry asphalt 0.7, wet 0.4, snow 0.2, ice 0.1); real ABS-equipped cars on dry roads reach 0.8–1.0 g. Grade, tyre wear and brake fade are not modelled.","sources":[{"name":"Wikipedia – Braking distance","url":"https://en.wikipedia.org/wiki/Braking_distance","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Stopping sight distance (AASHTO parameters)","url":"https://en.wikipedia.org/wiki/Stopping_sight_distance","type":"reference","retrieved_at":"2026-09-24"},{"name":"FHWA – Speed Concepts: Informational Guide, Chapter 4 (AASHTO stopping sight distance: 2.5 s perception-reaction time, 11.2 ft/s² deceleration)","url":"https://highways.dot.gov/safety/speed-management/speed-concepts-informational-guide/chapter-4-engineering-and-technical","type":"government","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"100 km/h, 1.5 s reaction, dry road","inputs":{"speed_km_h":100,"reaction_time_s":1.5,"road_condition":"dry"},"expected":{"speed_m_s":27.7778,"deceleration_m_s2":6.8647,"reaction_distance_m":41.67,"braking_distance_m":56.2,"total_stopping_distance_m":97.87,"total_stopping_distance_ft":321.1,"braking_time_s":4.046,"total_time_s":5.546},"url":"https://tttkmbb.com/api/v1/calculate/stopping-distance?speed_km_h=100&reaction_time_s=1.5&road_condition=dry"},{"name":"50 km/h, 1.0 s reaction, wet road","inputs":{"speed_km_h":50,"reaction_time_s":1,"road_condition":"wet"},"expected":{"reaction_distance_m":13.89,"braking_distance_m":24.59,"total_stopping_distance_m":38.48},"url":"https://tttkmbb.com/api/v1/calculate/stopping-distance?speed_km_h=50&reaction_time_s=1&road_condition=wet"}],"faq":[{"q":"Why does doubling the speed quadruple the braking distance?","a":"Kinetic energy grows with v², and the brakes remove it at a roughly constant force, so the distance v²/(2a) quadruples while the reaction distance only doubles."},{"q":"Which reaction time should I use?","a":"About 1.0–1.5 s for an alert driver expecting to brake; road designers use 2.5 s to cover most drivers in unexpected situations. Distraction or fatigue adds a second or more."}],"tags":["stopping distance","braking distance","reaction distance","thinking distance","how long to stop a car"],"related":[{"calculator_id":"speed-distance-time","reason":"Uniform motion during the reaction phase."},{"calculator_id":"acceleration","reason":"Deceleration from speed change and time."},{"calculator_id":"kinetic-energy","reason":"Energy the brakes must dissipate."}],"links":{"html":"https://tttkmbb.com/engineering/stopping-distance","markdown":"https://tttkmbb.com/engineering/stopping-distance.md","json":"https://tttkmbb.com/engineering/stopping-distance.json","api":"https://tttkmbb.com/api/v1/calculate/stopping-distance","schema":"https://tttkmbb.com/api/v1/calculators/stopping-distance","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:59:37Z","next_actions":[{"tool":"run_calculator","calculator_id":"stopping-distance","reason":"Run Stopping Distance Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/engineering/stopping-distance.md"}}