Experimenting with a Line2D road. Some very minor tweaks to Vehicle. Started work on an in-game 'Console' for debugging.

Assets/Graphics/road.png.import

+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/road.png-ba2e03c5623fd0c007ce17d39a38addd.stex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://Assets/Graphics/road.png"
+dest_files=[ "res://.import/road.png-ba2e03c5623fd0c007ce17d39a38addd.stex" ]
+
+[params]
+
+compress/mode=0
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/bptc_ldr=0
+compress/normal_map=0
+flags/repeat=1
+flags/filter=false
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=2
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+process/invert_color=false
+stream=false
+size_limit=0
+detect_3d=false
+svg/scale=1.0

Objects/Vehicle/Vehicle.gd

 var steering_angle = 0.0
 var engine_power = 0.0
 var breaking_power = 0.0
-var reverse = true
+var reverse = false
 
 onready var camera = $Camera2D
 
 	if speed >= traction_fast_speed:
 		traction = traction_fast
 	elif speed >= traction_slow_speed:
-		var d = speed / (traction_fast_speed - traction_slow_speed)
+		var d = (speed - traction_slow_speed) / (traction_fast_speed - traction_slow_speed)
 		traction = traction_slow + ((traction_fast - traction_slow) * d)
 	return traction
 
 	var heading = (fore_wheel - rear_wheel).normalized()
 	var traction = _generate_traction()
 	var d = heading.dot(velocity.normalized())
-	if d > 0:
+	if d > 0 and not (reverse or breaking_power > 0):
 		velocity = velocity.linear_interpolate(heading * velocity.length(), traction)
-	if d < 0:
+	if d < 0 and (reverse or breaking_power > 0):
 		velocity = velocity.linear_interpolate(-heading * velocity.length(), traction)
 	#velocity = heading * velocity.length()
 	rotation = (heading.angle() + deg2rad(90))

Scripts/Autoloads/consolectrl.gd

+extends Node
+
+signal message(msg)
+signal value_passed(name, v)
+
+const EMIT_RATE = 0.1
+
+var _timer_message : float = 0.0
+var _timer_pass_val : float = 0.0
+
+var _msg_buffer = []
+var _pass_val_buffer = []
+
+func _msgformat(msg : String, args : Array) -> String:
+	for i in range(0, args.size()):
+		msg = msg.format(args[i], "$" + String(i))
+	return msg
+
+func message(msg : String, args : Array = []) -> void:
+	if _timer_message <= 0.0:
+		emit_signal("message", _msgformat(msg, args))
+		_timer_message = EMIT_RATE
+	else:
+		_msg_buffer.append(_msgformat(msg, args))
+
+
+func pass_value(name : String, val) -> void:
+	emit_signal("value_passed", name, val)
+
+func _process(delta : float) -> void:
+	if _timer_message > 0.0:
+		_timer_message = max(0.0, _timer_message - delta)
+		if _timer_message == 0.0 and _msg_buffer.size() > 0:
+			emit_signal("message", _msg_buffer)
+			_msg_buffer = []
+

UI/Console/Console.tscn

+[gd_scene format=2]
+
+[node name="Console" type="CanvasLayer"]
+
+[node name="ScreenSplit" type="VBoxContainer" parent="."]
+anchor_right = 1.0
+anchor_bottom = 1.0
+__meta__ = {
+"_edit_use_anchors_": false
+}
+
+[node name="Messages" type="ScrollContainer" parent="ScreenSplit"]
+margin_right = 1920.0
+margin_bottom = 538.0
+size_flags_vertical = 3
+
+[node name="Label" type="Label" parent="ScreenSplit/Messages"]
+margin_bottom = 14.0
+
+[node name="Control" type="Control" parent="ScreenSplit"]
+margin_top = 542.0
+margin_right = 1920.0
+margin_bottom = 1080.0
+size_flags_vertical = 3

project.godot

 run/main_scene="res://World.tscn"
 config/icon="res://icon.png"
 
+[autoload]
+
+ConsoleCTRL="*res://Scripts/Autoloads/consolectrl.gd"
+
 [display]
 
 window/size/width=1920