Side Streets, Downtown Streets, Highways, Parkways and Freeways

Posted by PITHOCRATES - July 31st, 2013

Technology 101

In 20th Century our Subdivision Planners shifted from Automobile-Friendly to People-Friendly Designs

The automobile changed how we live.  Where once we crowded into crowded cites and worked close to where we lived today we don’t.  Instead choosing to live in sleepy suburbs.  Away from the noise and congestion of city life.  Where we can relax after work.  And on the weekend.  Enjoying a beer in the shade in our backyard.  Our little Shangri-La.  Come Monday morning, though, it’s back to the grind.  So we back our car out of the garage.  And drive out of our little residential community.

If you live in an older suburb that would be a drive down a straight road.  Running either north and south.  Or east and west.  Bringing you efficiently to a larger road.  That you can efficiently take to a larger road yet.  With a higher speed limit.  With many of us eventually taking that road to an onramp of an interstate freeway.  For that morning commute.  Quick.  And efficiently.  Thanks to our city and suburb planners making our cities and suburbs so automobile-friendly.

Soon everyone was driving so much that these roads got congested.  Including the ones in our sleepy little subdivisions.  With people racing down our side streets to get to those bigger roads.  Filling our little Shangri-La with the sounds of traffic.  And making it unsafe for our kids to ride their bicycles in the street.  Which is why somewhere around the middle of the 20th century our subdivision planners shifted from automobile-friendly to people-friendly.  Instead of grids of straight lines crossing other straight lines at neat right angles our roads in our subdivisions began to curve.  If you ever tried to cut through a subdivision and got so turned around that you ended up where you entered this is why.  To discourage people from driving through our sleepy little streets.  So we can relax with that beer in the shade.  And our kids can ride their bicycles safely in the streets in front of our homes.

Design Speed is the First Consideration when Designing a New Road

Cars are big and heavy.  Trucks are even bigger and heavier.  Yet millions of them safely share the same roads every day.  And few in a small car look twice at a semi truck and trailer stopped next to them at a traffic light.  Or give a second thought to an even bigger and heavier freight train crossing the road ahead of them while they sit at a railroad crossing.  All because of lines painted on the road.  Speed limit signs keeping us driving at the same speed.  And stop signs and traffic lights.  Which people observe.  And give the right-of-way to others.  While they wait their turn to proceed.  Except for trains.  They always have the right-of-way.  Because trains can’t stop as easily as a car or a truck.  And they pay a lot of money for that right-of-way.

As we left our neighborhoods and got onto the bigger roads and drove to the interstate freeway the speed limit got higher and higher.  And the faster large things go the more kinetic energy they build up.  Making it harder to stop.  And to control.  That’s why trains don’t stop for cars.  Cars stop for trains.  Emergency vehicles, like fire trucks and ambulances, get the right-of-way, too.  When we see their lights flashing and/or hear their sirens we pull to the curb and stop.  Because they’re speeding to an emergency and need a clear road.  But also because they are often traveling faster than the design speed of the road.

Yes, design speed.  Not the speed limit.  Two completely different things.  It’s the first consideration when designing a new road.  How fast will traffic travel?  Because everything follows from that.  Curves, grades, visibility, etc., these are all things that vary with speed.  Engineers will design a downtown street with a lot of vehicular and pedestrian traffic for lower speeds than they’ll design a country highway that connects two towns.  Also, lane width in a downtown street can be as narrow as 9 feet.  And they can have sidewalks adjacent to the curbs.  Allowing narrower streets for pedestrians to cross.  Freeways, on the other hand, have lanes that are 12 feet wide.  And have wide shoulders.  Because faster vehicles need more separation.  As they tend to waver across their lanes.  So this is another reason why we pull aside for emergency vehicles.  As they may approach or exceed the design speed of a road.  So we give them wider lanes by pulling over.  As well as giving them a less obstructive view of the road ahead.

The Modern Interstate Freeway System is Basically an Improved Parkway

Old 2-lane country highways had narrow lanes and narrow shoulders.  Making it easy to drift across the center line if distracted.  Or tired.  Into oncoming traffic.  If a person hugs the shoulder because he or she is nervous about fast-moving oncoming traffic they could drift over to the right.  Out of their lane.  And drop off of the shoulder.  Which could result in a loss of control.  Even a rollover accident.  And if you were stuck behind a slow-moving truck on a grade there was only one way around it.  Moving over into the lane of oncoming traffic.  And speeding up to get ahead of the truck before a car crashes head-on into you.  In fact, there used to be a passing lane.  A 3-lane highway with one lane traveling one direction.  One lane traveling in the other direction.  And a lane in the middle for passing.  Which worked well when only one person passed at a time.  But did not work so well when cars from each lane moved into the passing lane at the same time.  Running head-on into each other.  That’s why you won’t see a passing lane these days.  They are just too dangerous.

In the 20th century we started making roads for higher speeds.  Parkways.  The traffic travelling in either direction was separated by a median.  So you couldn’t drift into oncoming traffic.  There were no intersections.  Crossroads went over or under these parkways.  So traffic on the parkways didn’t have to stop.  They also had limited access.  On ramps and off ramps brought cars on and off, merging them into/out of moving traffic.  And unlike the old 2-lane country roads there were 2 lanes of traffic in each direction.  So if you wanted to pass someone you didn’t have to drive into oncoming traffic to go around a slower-moving vehicle.  And there was a paved shoulder.  So if a car had a flat tire they could limp onto the shoulder to change their tire.  Without interrupting the traffic on the parkway.  Of course, being on the shoulder of a parkway was not the safest place to be.  Especially if some distracted driver drifted onto the shoulder.  And crashed into your broken down car.

The modern interstate freeway system is basically an improved parkway.  They have wider lanes and wider shoulders.  Along the median and the outside right lane.  Instead of the typical Windsor Arch of the parkway they have bridges of concrete and steel.  Allowing greater spans over the roadway.  Keeping those shoulders wide even under the overpasses.  Grades are less steep.  And curves are less sharp.  Allowing little steering inputs at high speeds to control your vehicle.  Making for safer travel at even higher speeds.  And a much greater field of vision.  Even at night where there are no streetlights.  The road won’t change grade or curve so great beyond the length of your headlights.  Safely allowing a high speed even when you can’t see what’s up ahead.  Little things that you’ve probably never noticed.  But if you exit the interstate onto a curvy 2-lane highway with steep grades you will notice that you can’t drive at the same speed.  Especially at night.  In fact, you may drive well below the posted speed limit.  Because you can’t see the summit of the next hill.  Or the curve that takes you away from a sharp drop-off to a ravine below.  Like you find around ski resorts in the mountains.  The kind of highways you can’t wait to get off of and onto the safer interstate freeway system.  Especially in a driving snow storm.

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