diff --git a/dataserver.lisp b/dataserver.lisp
index b9b5311..4910391 100644
--- a/dataserver.lisp
+++ b/dataserver.lisp
@@ -11,6 +11,7 @@
 
 ;; Command-line arguments
 (defparameter *debugp* nil)
+(defparameter *gcp* nil)
 (defparameter *world-path* nil)
 ;; Note: do NOT change *server-port* and *server* at debug time
 (defparameter *server-port* nil)
@@ -32,6 +33,8 @@
 			       (tracks:import-data *nodedb*)
 			     (psetf *trackdb* ,tdb *trackdb-temp* ,tdbtemp)))
 	   (setf *trackdb* (tracks:import-data (ndb:import-data (savefilepath "ndb4.ls")))))
+       (when *gcp*
+	 #+sbcl(sb-ext:gc :full t))
        (hunchentoot:acceptor-log-message *server* :info "Database updated"))))
 
 (defmacro mainloop ()
@@ -42,6 +45,7 @@
     (setf *world-path* (ensure-world-path (car argv)))
     (setf *server-port* (coerce (parse-integer (cadr argv)) '(integer 0 65535)))
     (setf *debugp* (member "--debug" (cddr argv) :test #'string=))
+    (setf *gcp* (member "--force-periodic-gc" (cddr argv) :test #'string=))
     (setf *server* (make-instance 'easy-routes:routes-acceptor :port *server-port*))
     (register-routes)
     (register-debugging-routes)
@@ -156,6 +160,7 @@
 
 (defun start-server ()
   (tracks:init-tracks)
+  (load-data)
   (hunchentoot:start *server*)
   ;; loop until an error occurs
   (if *debugp* (mainloop) (handler-case (mainloop)
diff --git a/tracks/conns.lisp b/tracks/conns.lisp
index 29a78b5..5039dca 100644
--- a/tracks/conns.lisp
+++ b/tracks/conns.lisp
@@ -1,5 +1,8 @@
 (in-package :tracks)
 
+(defparameter *dir-shared* nil)
+(defparameter *conns-shared* nil)
+
 (defstruct trackside
   (:pos (error "no coordinates specified") :type aux:v3d)
   (:side (error "no side specified") :type (integer 0 15)))
@@ -34,46 +37,69 @@
   (print-unreadable-object (obj s)
     (format s "FROM ~a TO ~a" (conns-from obj) (conns-to obj))))
 
-(defmacro dir (c &optional r)
-  `(make-dir :c (or ,c 0) :r (or ,r 0)))
+(defun init-shared-dirs ()
+  (setf *dir-shared* (make-array 32 :element-type 'dir :adjustable nil :initial-contents
+				 (loop for i from 0 to 31 collect
+				      (make-dir :c (ash i -1) :r (mod i 2)))))
+  (setf *conns-shared* (coerce (loop for i from 0 to 1023 collect
+				    (make-conns :from (aref *dir-shared* (ash i -5))
+						:to (aref *dir-shared* (mod i 32))))
+			       '(vector conns 1024))))
 
-(defmacro conns (c1 c2 &optional r1 r2)
-  `(make-conns :from (dir ,c1 ,r1) :to (dir ,c2 ,r2)))
+(defmacro dir (c &optional r shared)
+  (alexandria:with-gensyms (cc rc)
+    `(let ((,cc (the (integer 0 15) ,c)) (,rc (the (integer 0 1) (or ,r 1))))
+       (if ,shared (aref *dir-shared* (+ (* 2 ,cc) ,rc))
+	   (make-dir :c ,cc :r ,rc)))))
 
-(defmacro conns-t ((c1 &body cb) (&optional r1 &body rb))
+(defmacro conns (c1 c2 &optional r1 r2 shared)
+  (alexandria:with-gensyms (cf ct rf rt)
+    `(let ((,cf (the (integer 0 15) ,c1)) (,ct (the (integer 0 15) ,c2))
+	   (,rf (the (integer 0 1) (or ,r1 0))) (,rt (the (integer 0 1) (or ,r2 0))))
+       (if ,shared (aref *conns-shared* (+ (ash ,cf 6) (ash ,rf 5) (ash ,ct 1) ,rt))
+	   (make-conns :from (dir ,c1 ,r1) :to (dir ,c2 ,r2))))))
+
+(defmacro dirs->conns (from to &optional shared)
+  (alexandria:once-only
+   (from to)
+   `(if ,shared (conns (dir-c ,from) (dir-c ,to) (dir-r ,from) (dir-r ,to) t)
+	(make-conns :from ,from :to ,to))))
+
+(defmacro conns-t ((c1 &body cb) (&optional r1 &body rb) &optional shared)
   ``(,,@(loop for c in cb and ri = rb then (cdr ri) for r = (car ri)
-	   collect `(conns ,c1 ,c ,r1 ,r))))
+	   collect `(conns ,c1 ,c ,r1 ,r ,shared))))
 
-(defmacro conns-x ((&body cb) (&body rb))
+(defmacro conns-x ((&body cb) (&body rb) &optional shared)
   ``(,,@(loop for (c1 c2) on cb by #'cddr and r = rb then (cddr rb)
 	   for r1 = (car r) and r2 = (cadr r)
-	   collect `(conns ,c1 ,c2 ,r1 ,r2))))
+	   collect `(conns ,c1 ,c2 ,r1 ,r2 ,shared))))
 
-(defmacro adjust-dir (dir diff)
+(defmacro adjust-dir (dir diff &optional shared)
   (alexandria:once-only
    (dir)
-   `(dir (mod (+ 16 (or ,diff 0) (dir-c ,dir)) 16) (dir-r ,dir))))
+   `(dir (mod (+ 16 (or ,diff 0) (dir-c ,dir)) 16) (dir-r ,dir) ,shared)))
 
-(defmacro adjust-conns (conns diff)
+(defmacro adjust-conns (conns diff &optional shared)
   (alexandria:once-only
-   (conns diff)
-   `(make-conns :from (adjust-dir (conns-from ,conns) ,diff)
-		:to (adjust-dir (conns-to ,conns) ,diff))))
+   (conns diff shared)
+   `(dirs->conns (adjust-dir (conns-from ,conns) ,diff ,shared)
+		 (adjust-dir (conns-to ,conns) ,diff ,shared)
+		 ,shared)))
 
-(defmacro adjust-conns-list (clist diff)
+(defmacro adjust-conns-list (clist diff &optional shared)
   (alexandria:with-gensyms (i)
     (alexandria:once-only
-     (diff)
-     `(loop for ,i in ,clist collect (adjust-conns ,i ,diff)))))
+     (diff shared)
+     `(loop for ,i in ,clist collect (adjust-conns ,i ,diff ,shared)))))
 
-(defmacro adjust-dir-with-param2 (dir param2)
-  `(adjust-dir ,dir (* 4 ,param2)))
+(defmacro adjust-dir-with-param2 (dir param2 &optional shared)
+  `(adjust-dir ,dir (* 4 ,param2) ,shared))
 
-(defmacro adjust-conns-with-param2 (conns param2)
-  `(adjust-conns ,conns (* 4 ,param2)))
+(defmacro adjust-conns-with-param2 (conns param2 &optional shared)
+  `(adjust-conns ,conns (* 4 ,param2) ,shared))
 
-(defmacro adjust-conns-list-with-param2 (clist param2)
-  `(adjust-conns-list ,clist (* 4 ,param2)))
+(defmacro adjust-conns-list-with-param2 (clist param2 &optional shared)
+  `(adjust-conns-list ,clist (* 4 ,param2) ,shared))
 
 (defmacro apply-dir-to-v3d (pos dir)
   (alexandria:with-gensyms (h)
diff --git a/tracks/database.lisp b/tracks/database.lisp
index d07a762..a9d45d0 100644
--- a/tracks/database.lisp
+++ b/tracks/database.lisp
@@ -77,7 +77,7 @@
     (ndb:loopdb
      (ndb pos node param2)
      (alexandria:when-let ((clist (gethash node *track->conns*)))
-       (setf (gethash pos tmpdb) (adjust-conns-list-with-param2 clist param2))))
+       (setf (gethash pos tmpdb) (adjust-conns-list-with-param2 clist param2 t))))
     (loop for pos being the hash-keys of tmpdb using (hash-value clist)
        for dirs = (conns-list-dirs clist)
        for connects = (make-empty-connects) do
diff --git a/tracks/registration.lisp b/tracks/registration.lisp
index 837bb2a..2973e32 100644
--- a/tracks/registration.lisp
+++ b/tracks/registration.lisp
@@ -13,7 +13,7 @@
      (names conns)
      `(loop for ,i = 0 then (1+ ,i) for ,s in `("" "_30" "_45" "_60")
 	 for ,n = (loop for ,j in ,names collect (concatenate 'string ,j ,s))
-	 do (register-tracks ,n (adjust-conns-list ,conns ,i))))))
+	 do (register-tracks ,n (adjust-conns-list ,conns ,i t))))))
 
 (defmacro prefix-names (prefix &body names)
   (alexandria:once-only
@@ -35,59 +35,60 @@
 (defmacro register-default-tracks (prefix)
   `(register-rotatable-track-with-preset
     ,prefix
-    (("st") (conns-t (0 8) ()))
-    (("cr") (conns-t (0 7) ()))
-    (("swlst" "swlcr") (conns-t (0 8 7) ()))
-    (("swrst" "swrcr") (conns-t (0 8 9) ()))))
+    (("st") (conns-t (0 8) () t))
+    (("cr") (conns-t (0 7) () t))
+    (("swlst" "swlcr") (conns-t (0 8 7) () t))
+    (("swrst" "swrcr") (conns-t (0 8 9) () t))))
 
 (defmacro register-y-turnout-tracks (prefix)
   `(register-rotatable-track-with-preset
     ,prefix
-    (("l" "r") (conns-t (0 7 9) ()))))
+    (("l" "r") (conns-t (0 7 9) () t))))
 
 (defmacro register-3way-turnout-tracks (prefix)
   `(register-rotatable-track-with-preset
     ,prefix
-    (("l" "s" "r") (conns-t (0 7 8 9) ()))))
+    (("l" "s" "r") (conns-t (0 7 8 9) () t))))
 
 (defmacro register-slope-tracks (prefix)
   `(register-rotatable-track-with-preset
     ,prefix
-    (("vst1" "vst31" "vst32") (conns-t (8 0) (0 0)))
-    (("vst2" "vst33") (conns-t (8 0) (0 1)))))
+    (("vst1" "vst31" "vst32") (conns-t (8 0) (0 0) t))
+    (("vst2" "vst33") (conns-t (8 0) (0 1) t))))
 
 (defmacro register-straightonly-tracks (prefix)
   `(register-rotatable-track-with-preset
     ,prefix
-    (("st") (conns-t (0 8) ()))))
+    (("st") (conns-t (0 8) () t))))
 
 (defmacro register-perp-xing-tracks (prefix)
   `(register-rotatable-track-with-preset
     ,prefix
-    (("st") (conns-x (0 8 4 12) ()))))
+    (("st") (conns-x (0 8 4 12) () t))))
 
 (defmacro register-90+x-xing-tracks (prefix)
   `(register-track-with-preset
     ,prefix
-    (("30l") (conns-x (0 8 1 9) ()))
-    (("45l") (conns-x (0 8 2 10) ()))
-    (("60l") (conns-x (0 8 3 11) ()))
-    (("60r") (conns-x (0 8 5 13) ()))
-    (("45r") (conns-x (0 8 6 14) ()))
-    (("30r") (conns-x (0 8 7 15) ()))))
+    (("30l") (conns-x (0 8 1 9) () t))
+    (("45l") (conns-x (0 8 2 10) () t))
+    (("60l") (conns-x (0 8 3 11) () t))
+    (("60r") (conns-x (0 8 5 13) () t))
+    (("45r") (conns-x (0 8 6 14) () t))
+    (("30r") (conns-x (0 8 7 15) () t))))
 
 (defmacro register-diag-xing-tracks (prefix)
   `(register-track-with-preset
     ,prefix
-    (("30l45r") (conns-x (1 9 6 14) ()))
-    (("60l30l") (conns-x (3 11 1 9) ()))
-    (("60l45r") (conns-x (3 11 6 14) ()))
-    (("60l60r") (conns-x (3 11 5 13) ()))
-    (("60r45l") (conns-x (5 13 2 10) ()))
-    (("60r30r") (conns-x (5 13 7 15) ()))
-    (("30r45l") (conns-x (7 15 2 10) ()))))
+    (("30l45r") (conns-x (1 9 6 14) () t))
+    (("60l30l") (conns-x (3 11 1 9) () t))
+    (("60l45r") (conns-x (3 11 6 14) () t))
+    (("60l60r") (conns-x (3 11 5 13) () t))
+    (("60r45l") (conns-x (5 13 2 10) () t))
+    (("60r30r") (conns-x (5 13 7 15) () t))
+    (("30r45l") (conns-x (7 15 2 10) () t))))
 
 (defun init-tracks ()
+  (init-shared-dirs)
   (setf *track->conns* (make-hash-table :test #'equal))
   (register-default-tracks "advtrains:dtrack")
   (register-y-turnout-tracks "advtrains:dtrack_sy")